NATIONAL ASSOCIATION OF GEOLOGY TEACHERS
EAST-CENTRAL SECTION

Annual Meeting
April 1 - 2, 1966

Indiana University
Bloomington, Indiana

Field Trip
Saturday, April 2, 1966

SOME GEOLOGICAL ASPECTS OF THE CARBONIFEROUS OF
SOUTHERN INDIANA

Compiled by
Thomas E. Hendrix

(page) 2.

Preface

You are invited to join us on a tour of some of the better known, more important and, we hope, more interesting aspects of the geology of Southern Indiana. This geological potpourri contains ingredients that should please both the research-minded university professor and the secondary school earth science teacher. Its emphasis, of course, is geology, but here and there where it appears appropriate you will read or hear about engineering, economic, political, and (in weak moments) philosophical things that play an important role in the study of Indiana's geological heritage and the utilization of her mineral resources.
This guidebook contains much of the basic information you will need to fully understand the detail you will see along the route, and to tie this detail into the framework of the regional geological picture. An attempt has been made to bring to your attention the latest information on a given subject, but by no means should this guidebook be considered as a progress report of the geological research being done in the area. In putting this Guidebook together the compiler has made liberal use of published and unpublished reports of Indiana geology, and he has drawn heavily on the knowledge of colleagues at Indiana University who are engaged in geological research in Southern Indiana. However, any errors of omission or misinterpretation are solely the responsibility of the compiler.

(page) 3.

Figure 1.

Itinerary
             STOP                                     DISCUSSION LEADERS

1. Monroe Reservoir, Dam & Spillway, 8:00-9:00 a.m.     Thomas E. Hendrix

2. P.M.&B. Dimension Stone Quarry, 9:15-9:45 a.m.       John B. Patton

3. U.S.& National Gypsum Company Mines, 10:15-11:30 a.m. Company 
                                                          Representatives

    ----------------------End of Half-Day Option----------------------

Lunch - Linton, Indiana 12:30-1:15 p.m.
4. Minnehaha Coal Strip Mine, 1:30-3:00 p.m. Charles E. Wier 5. Illinois Central RR Cut, Solsberry, 3:45-5:00 p.m. Thomas G. Perry, Thomas E. Hendrix Figure 1. -- Location map and itinerary

(page) 4.

Geological Setting

This trip covers an area of about 900 square miles in southern and southwestern Indiana. The bedrock consists of sedimentary rocks of Mississippian and Pennsylvanian ages, arranged into formations, groups, and series as shown on the stratigraphic chart, figure 2, and exposed in northwestward-southeastward trending outcrop belts as seen on the geological map, figure 3. The area lies at the eastern margin of the Illinois Basin. Regional dips are about 30 feet to-the-mile to the southwest.
Most of the area lies south of the Illinoisan glacial boundary. As a result the topography, physiography and soils are more or less directly related to the underlying bedrock, and the whole area takes on the appearance of a gigantic geological layer cake, tilted slightly to the southwest and dissected by differential erosion into a series of alternating uplands and lowlands. In general the upland surfaces are underlain by relatively resistant sandstones and siltstones and the lowlands are underlain by limestones or (west of the glacial boundary) glacial drift and outwash.
Malott (1922) recognized in southern Indiana six major physiographic provinces, four of which will be seen on this trip. These provinces are shown in figure 4. A brief description of each of the four physiographic provinces seen on the trip is given below.

NORMAN UPLAND. -- The Norman upland (Malott, 1922, p. 90-94) is an asymmetric highland region underlain by siltstones, sandstones, and shales of the Borden Group (Lower Mississippian). The eastern edge of the upland is a prominent escarpment (the Knobstone escarpment) that rises 300 to 600 feet above the valleys and lowlands to the east. Within the Norman upland gradation by running water has carved steep-walled, narrow-bottomed valleys into the gently

(page) 5.

westward-dipping rocks of the Borden Group, and has produced high local relief. Hilltops have altitudes ranging from 900 to more than 1000 feet and generally are considered to be the remnants of a peneplain (the Lexington Surface) which was uplifted in Late Tertiary time.

To the west the Norman upland merges almost imperceptibly down the dip slope of the Borden Group with the adjoining lowland.

MITCHELL PLAIN. -- Ground water solution acting on the thick sequence of Middle Mississippian limestones has created a lowland region called the Mitchell Plain (Beede, 1910, p. 95; Malott, 1922, p. 94-98, 187-215). Numerous caves, sinkholes, dolines, sinking streams, uvalas, and other Karst features are well developed in this physiographic province south of Bloomington.

The Mitchell plain is developed principally on the dip slope of the St. Louis limestone but includes the Salem and Ste. Genevieve limestones. Its surface slopes westward from an altitude of about 900 feet at the eastern edge to about 750 feet at the base of the Chester escarpment to the west.

CRAWFORD UPLAND. -- The Crawford upland (Malott, 1922, p. 98-102, 215-247) is another asymmetric highland with a steep eastern escarpment and a gentle westward sloping surface. The area is underlain by sandstones, shales, and limestones of the Chester Series (Upper Mississippian). The eastern edge of the Crawford upland is highly irregular and is characterized by Chester outliers and karst valley reentrants. Many of the larger and more accessible caverns are found near the eastern edge of the Crawford upland where insoluble sandstones of the Chester Series form protective caps over solution cavities in the Meramecian limestones.

The upland itself is maturely dissected by stream erosion. Local relief is as high as 400 feet. The western part of the upland is underlain by somewhat less resistant rocks of Pennsylvanian age and consequently the local relief is more subdued.

(page) 6.

WABASH LOWLAND. -- A broad, low, flat region underlain by shales and coals of Pennsylvanian age and mantled with varying thicknesses of glacial drift, outwash, and wind-blown sand characterizes the Wabash lowland. Surface elevations average about 500 feet. The eastern edge of the Wabash lowland is transitional with the Crawford upland.

(page) 7. Figure 2.

(page) 8. Figure 3.

(page) 9. Figure 4.

(page) 10.

ROAD LOG

Caravan will form in parking lot behind Geology Building. Turn left out of parking lot, left again onto Forest Street and proceed one block to Tenth Street. Turn right (west) onto Tenth Street and proceed to Washington Street. Turn left onto Washington Street and drive south through town to First Street. Turn right on First Street and proceed one block to South Walnut (Indiana Highway 37). Turn left onto Walnut and proceed south out of town. Road log begins at city limits where Monon spur crosses Highway 37.

MILEAGE

    0.0	   Railroad spur lines cross Indiana Highway 37.

    0.4    New Bloomington Senior High School on left (east). Bedrock is 
           Salem Limestone.

    1.1    Red-colored, clay-rich TERRA ROSA soil on right.  Typical of 
           residual soils developed on Mississippian limestones in 
           Bloomington region.  Route is south along the strike of the 
           bedrock formations.  Physiographic region known as MITCHELL 
           PLAIN.

    2.4	   Ascend small hill; Canada Motel at crest of hill on left.  
           Ahead to the south about one mile hoisting cranes of building 
           stone quarries rise above the trees.  Road descends into 
           valley of Jackson Creek.

    3.2	   Cross bridge over Jackson Creek and go under Monon railroad 
           bridge.

    3.25   Medium-bedded limestone exposed on left.  HARRODSBURG LIMESTONE.

    4.1    Low exposure of massively-bedded limestone on left.  SALEM
           LIMESTONE.

    4.2	   Same on right.

    4.8	   Cross abandoned quarry spur line of Monon railroad.

    5.0	   Begin ascent of hill.  Blocks of Salem limestone in abandoned 
           dimension stone quarry on right.

    5.1	   Blue-gray, medium- to thin-bedded limestone at top of hill on 
           right.  Thin tan shale partings.  ST. LOUIS LIMESTONE.
(page) 11.

MILEAGE

    5.4	    Descend hill.  Low exposures of SALEM on right, near top of 
            formation.

    5.7	    Road goes through wire-sawed road cut in SALEM LIMESTONE.  
            Notice vertical joints widened by ground water solution.

    6.0	    ST. LOUIS LIMESTONE.  Shaly limestone on left.  Scar of 
            recurring slump in soil over limestone on right.  For next 
            2½ miles road is along partially dissected upland surface 
            underlain by upper part of Salem limestone and lower part of 
            St. Louis limestone.  Soil developed from St. Louis usually 
            contains chert fragments.

    8.5	    Begin descent into valley of Clear Creek.  Start at top of SALEM
            LIMESTONE on left.

    8.8	    Good exposures of SALEM LIMESTONE.  Massive, cross-bedded, 
            coarse-grained limestone on left.

    9.0	    Approximate base of SALEM LIMESTONE at base of tan massive, 
            cross-bedded layer on left.  Medium to massive bedded blue-gray 
            limestone below--HARRODSBURG LIMESTONE.

    9.1 to
    9.3	    Excellent exposures of HARRODSBURG LIMESTONE on left.  Medium 
            bedded to massive bedded limestone at top and thin to medium 
            bedded crinoidal limestone and gray calcareous shale at base.  
            White spots on face of outcrop are geodes.  Base of Harrodsburg
            at base of exposure on left.

    9.4	    Cross bridge over Monon railroad.  Start across wide flood 
            plain of Clear Creek.  Most of the streams in this part of 
            Indiana that had access to the glacial drift and outwash to the 
            north have flood plains much broader than the present streams 
            could have formed.

    9.6	    Cross bridge over Clear Creek.

    9.7 to
    9.8	    Low exposures of brown or gray-brown siltstone BORDEN GROUP.  
            Dangerous turn ahead!

    9.85    Village of Harrodsburg.  Turn left off Indiana 37 onto county 
    (0.00)  road to Monroe Reservoir.  Rough surface and narrow road. 
    CHECK SPEEDOMETER

    0.0 to
    0.5	    Road is along south valley wall of Clear Creek at an elevation 
            near the base of the Harrodsburg limestone.

    0.5	    Cross Monon railroad tracks (slowly!) and descend to flood 
            plain of Clear Creek again.
(page) 12.

MILEAGE

    0.7	    Cross Clear Creek and start up steep hill.  Clear Creek flows 
            southeastward (left to right) at this point and joins Salt Creek 
            about one mile below the Monroe Reservoir dam.

    0.8 to
    0.9	    HARRODSBURG LIMESTONE exposed along road to right.  This 
            exposure is not for the driver to see!

    1.2	    Turn right onto access road leading to dam and spillway, Monroe 
            Reservoir.  Notice good TERRA ROSA soil along road.

    1.4	    View of Monroe Reservoir (Lake Monroe) to left.  Point of land 
            directly across lake to the northeast is Kelly Point.

    1.6	    Turn right on road leading to observation point.  View of the 
            dam straight ahead.  Also good exposures of massive, cross-bedded
            SALEM LIMESTONE at turn.  We will return to this exposure for a 
            short stop after the initial stop at observation point.

    1.9	    Turn into parking area for Stop 1, Monroe Reservoir.

Stop l.--Monroe Dam and Reservoir

Introduction. -- The Monroe Reservoir project was selected for construction under the general authorization for flood control in an Act of Congress approved July 3, 1958, and assigned to the U.S. Army, Corps of Engineers. Preliminary topographic, engineering, and geologic investigations were carried out by the Corps of Engineers and by the Flood Control and Water Resources Commission, State of Indiana, working in part through the State Geological Survey. In 1955 the State Geological Survey made measurements of the thickness of valley fill at the dam site and conducted a drilling program on Kelly Ridge east of the dam site to determine the nature of the bedrock surface at the prospective spillway sites.

Construction of the dam and spillway was started in November, 1960, and the project was dedicated in October, 1964. Total cost of the project was $14,700,000 of which $7,950,000 or 54.1 percent was assumed by the State of Indiana. The reservoir is operated for the combined purposes of flood control and low-flow regulations.

GEOLOGY AT THE DAM SITE AND SPILLWAY. -- Bedrock formations at the dam site and spillway consist of siltstones of the Borden Group and the Harrodsburg and Salem limestones. Terrace and flood-plain deposits overlie the bedrock along the lower parts of the valley walls. Winslow, Gates, and Melhorn (1960) arranged the bedrock and unconsolidated deposits into four map units according to their lithology, origin, and engineering characteristics as follows:

QUATERNARY SYSTEM

UNIT THICKNESS (feet) DESCRIPTION 4 0 - 69 Flood-plain deposits. Brown and blue-gray clayey silts with admixed sands.

(page) 13. Figure 5.

(page) 14.

QUATERNARY SYSTEM (continued)

UNIT THICKNESS (feet) DESCRIPTION 3 0 - 70+ Terrace deposits. Alluvial clayey sandy silts, gravelly in part; colluvial clayey gravels; and lacustrine clayey silts. Coarse material composed of chert and geode fragments, granite, quartzite, and siltstone pebbles.
MISSISSIPPIAN SYSTEM
      2	      130	       Salem limestone. Fine- to coarse-grained,
			       porous bioclastic limestone. Cross-bedded.
			       Top not exposed.

			       Harrodsburg limestone. Lower part impure
			       crinoidal limestone interbedded with dark
			       calcareous siltstone; geodes abundant;
			       upper part coarse crystalline medium-
			       bedded limestone. About 70 feet thick in
			       slope west of dam.

      1        80              Borden Group. Edwardsville formation. Tan
            (exposed)	       massive siltstone, 65 feet thick at base of
			       exposure; 15 feet of blue-gray shaly sandy
			       siltstone at top.

The top of the Borden Group occurs at an elevation of 590-600 feet above sea level at the dam and spillway, or about 40 feet above the flood pool stage of the reservoir. All bedrock units in the region rise in elevation to the east-northeastward at a rate of 30-feet-to-the-mile, so that the water level in the reservoir is everywhere below the base of the limestones. Because of its low permeability the Borden Group provides an excellent "container" for the waters of the reservoir. Several thin limestone beds and thicker biohermal masses are present in the upper part of the Borden Group in the reservoir area, but none are thick enough, cavernous enough, or continuous enough to present any serious leakage problems. Six miles east of the dam the Borden is broken by the Mt. Carmel fault, a NNW-SSE trending, steeply-dipping normal fault with about 80 feet vertical displacement (east side up) but again no serious leakage problem is encountered.

Both the Harrodsburg and Salem limestones contain many solution-widened joints and bedding surfaces and therefore are unsuitable as "containers" for the reservoir. A residual soil rich in clay and averaging about 12 feet in thickness overlies the limestones along the tops of the ridges on either side of the dam.

Numerous terrace deposits are present along the valley walls of Salt Creek and its tributaries. See the geologic map, figure 5. Parts of many of the terraces above the dam will be below water at normal pool stage (538 feet) but no leakage problem is expected.

(page) 15.

Tests conducted by the Corps of Engineers on the unconsolidated valley-fill materials have shown that they will provide a stable, impermeable base for the dam.

ENGINEERING ASPECTS .-- PROJECT DATA (taken from Corps of Engineers pamphlet)

STREAM
Drainage area above dam, square miles 441
Maximum flow of record at dam site (1913 c.f.s.) 37,000
Mean Flow at dam site (1955 c.f.s.) 483

DAM
Type of structure: Impervious clay core with rock she11
Top elevation 574
Maximum height above stream bed, feet 93
Length, feet 1,400
Maximum base width, feet 840
Quantity of earth fill, cu. yds. 1,127,000

OUTLET WORKS
Type of Structure Reinforced concrete Circular Conduit
Size 12 feet diameter
Total Length, feet 630
Control 3 slide gates 3.75 feet wide by 12 feet high
Design discharge capacity (maximum) c.f.s. 5,140

SPILLWAY
Type Open cut through Kelly Ridge
Base Width, feet 600
Length, feet 750
Quantity of excavation, cu. yds. 992,000
Design discharge capacity, c.f.s. 73,760

RESERVOIR
                                	Area	  Storage*	Pool 
                       Elevation	(Acres)	 (Acre-feet)	Length
Silt Pool 515 3,280 22,300 22
Low-flow regulation pool 515-538 10,750 159,900 22-37
Flood control pool 538-556 18,450 258,800 37-44
Low-flow regulation storage in inches of runoff 6.8
Flood control storage in inches of runoff 11.0
The reservoir will be maintained at or near low-flow regulation pool level, except when water is stored for flood control.
* One acre-foot = 325,850 gallons of water

(page) 16.

The dam is an earthen structure with an impermeable clay core, and rests on the unconsolidated valley-fill material. The northeastern abutment is against the thin terrace deposits that mantle a bedrock bench underlain by siltstones of the Borden Group. The southwestern abutment lies directly against siltstone of the Borden Group. The outlet conduit beneath the dam on the southwestern side is also founded on siltstone of the Borden Group.

Clay for the core of the dam comes from the lower and middle zones (B horizon) of the soil above the limestones on Kelly Ridge east of the dam. The core is supported on both the upstream and downstream sides by thick pads of crushed siltstone and limestone removed from the spillway.

(page) 17.

Return via county road to Indiana Highway 37 at Harrodsburg. Turn left (south) onto 37.

CHECK SPEEDOMETER
MILEAGE

    0.0      Intersection of county road and Indiana Highway 37.

    0.1      Contact of BORDEN GROUP and HARRODSBURG LIMESTONE on left at 
             base of sycamore tree.

    0.6      Good exposure of SALEM LIMESTONE on right.  Massive 
             tan-colored, cross-bedded limestone.  View to the left of 
             the extensive flood plain of Clear Creek.

    0.7	     Begin descent into valley of small tributary to Clear Creek.
             Pass through lower part of SALEM and the HARRODSBURG to the 
             base at about stream level.

    1.2	     Cross stream and start ascent of south valley wall.  The road 
             goes back up through the HARRODSBURG and SALEM.  Exposures 
             mainly on right.  Base of the Salem contains numerous 
             PENTREMITES at this locality.

    1.5	     Base of ST. LOUIS LIMESTONE exposed along road on the right.

    1.7	     ST. LOUIS limestone again on right.  Cherty TERRA ROSA on 
             left.  Road climbs onto broad upland surface (still in Mitchell 
             plain) underlain by St. Louis limestone.  Prominent ridge several
             miles off to the right (west) is the Chester escarpment, the 
             eastern edge of the Crawford upland.

             On either side of the road for the next 2½ miles are 
             numerous round, elliptical, and irregular-shaped depressions 
             (sinkholes) caused by groundwater solution in the St. Louis 
             limestone and subsequent collapse of the overlying bedrock and 
             soil.

    4.0      Road to Guthrie and Monroe Reservoir on left.

    5.2	     Low exposures of SALEM LIMESTONE along road on right.  Near 
             top of formation.

    5.4	     Farm pond in small valley on right.  Farmer has had indifferent 
             success keeping water impounded behind dam.  Bedrock, of course, 
             won't contain surface water in this area, and only if soil is 
             left undisturbed will farm ponds hold water.  Often, however, the 
             farmer scrapes off the soil in the impounding area to make the 
             dam, thus defeating his own purpose.  Geological salesmanship is 
             needed here.

(page) 18.

MILEAGE

    5.6	     Descend into valley of small stream.  Go down section again 
             through SALEM and HARRODSBURG limestones.

    6.1	     Cross stream and start back up through section.

    6.5	     Basal part of the ST. LOUIS LIMESTONE exposed along both 
             sides of the road at top of hill.

    6.8	     Sign to village of Needmore on right.

    7.7	     View of extensive dimension stone quarry operation ahead and on 
             left.  Be prepared to make left turn off highway onto quarry 
             road.

    8.0      Abandoned dimension stone quarries on right.

    8.1      Turn left off Highway 37 onto quarry road.  Follow lead car and 
             watch traffic!  Dangerous turn.  Follow lead car down hill and 
             park at turnaround near quarry floor.
---
Stop 2. -- P M & B Dimension Stone Quarry - Salem Limestone

Introduction.--The P M & B quarry is part of a complex of limestone dimension stone quarries near Oolitic owned and operated by the Indiana Limestone Corporation. The formation utilized is the Salem limestone.

In this quarry the Salem is overlain by about 5 feet of reddish-brown clayey soil, and about 15 feet of blue-gray argillaceous limestone and shale of the St. Louis formation. In addition, the top 15-18 feet of the Salem is a blue-gray to gray, fine-grained limestone with admixed carbonaceous material, and known locally as "bastard stone." The soil, St. Louis Limestone and "bastard stone" are removed and discarded as waste material. Much of the worthless cap rock and some of the valuable stone is marred by grikes-- solution-widened joints or bedding surfaces commonly filled with clayey soil. Several grikes are nicely displayed in the west wall of the quarry.

The Salem limestone has many qualities which make it admirably suited as a building stone. It is uniform in texture and color. It does not discolor upon weathering, it is soft, yet strong, and it occurs in massive beds where bedding planes are often ten or more feet apart. Below the zone of grike formation it is also relatively free of joints or other fissures.

The section listed below was measured by the Indiana Geological Survey and appears in the Geological Survey Field Conference Guidebook on the Salem, (Perry, Smith, and Wayne, 1954, p. 33-34).

(page) 19.

Salem Limestone                                          Thickness
                                                           in feet
     7   Limestone: Gray, fine-grained, noncrystalline.
         Medium-bedded argillaceous stone has conchoidal
         fracture and contains a few microfossils.            10.0

     6   Limestone: Gray, fine-grained, noncrystalline. Unit 
         consists of one bed that contains a few crystals 
         of calcite and has a banded appearance because of
         the inclusion of darker material.                     8.2

     5   Limestone: Buff to tan, medium-grained, crystalline, 
         slightly argillaceous.  Gray, coarser grained and 
         porous lenses occur in association with stylolites.
         Fossils more sparse than in underlying units.        11.9

     4   Limestone: Very light-buff, fine-grained, crystal-
         line and bioclastic. Unit consists of a massive, 
         homogeneous bed whose crystallinity and induration 
         increase upward; a stylolite bounds the top of the
         unit.                                                13.7

     3   Limestone: Light-buff, coarse-grained, bioclastic,
         porous; organic remains are cemented by finely 
         crystalline material.  Variation in size of bio-
         clastic grains in inclined beds indicate sorting.     5.7

     2   Limestone: Dark-gray and buff, fine- to coarse-
         grained, bioclastic, porous.  Crystalline 
         material partially fills the interspaces in this
         bioclastic rock.                                     18.6

     1   Limestone: Buff-brown, coarse-grained, bioclastic;
         inclined bedding occurs in upper 2.5 feet.            7.8
                                                             _______
     Total thickness of exposed Salem limestone               75.9
In this area the Salem limestone is a medium- to coarse-grained bioclastic limestone. Nearly all the skeletal material is fragmental and includes, in order of decreasing abundance, bryozoans, echinoderms, and ENDOTHYRA.

Chemical analysis of the Salem limestone at this locality yields the following figures (average of five analyses):
	CaCO3            97.90 percent
	MgCO3             1.68   "
	SiO2              0.86   "
	Al2O3             0.067  "
	Fe2O3             0.161  ""
	MnO              0.006   "
	S                0.039   "
       ________________________________________
                       100.713 Percent
	CO2             43.5 Percent

(page) 20.

Pettijohn, Potter, and Siever (1965, p. 157) conclude that the Salem limestone is a well-sorted shallow-shelf marine sand in which sand wave migration perpendicular to the shoreline was the major factor in sediment transport. This interpretation is drawn, in large part, from a study of crossbedding in the Salem, the results of which are shown on figure 6.

QUARRY OPERATIONS. -- After the overburden and worthless rock is removed the upper surface of the rock is smoothed off and channeling machines are set up on four-foot wide tracks down the length and across the breadth of the quarry floor. The channeling machines consist of one or two chisel-bit steel bars attached to a piston that is usually steam driven. The channeling machines work their way back and forth across the quarry floor chiselling a vertical groove several inches wide and ten to twelve feet deep in the stone, producing rectangular-shaped blocks four feet wide and of varying lengths. Occasionally a wire saw is used to make the vertical cuts in the stone.

After the channeling process is completed, the rectangular blocks of stone--free now on three sides--are wedged out at the base. The first block, of course, must be wedged out from the top and often a good deal of the stone is wasted. Once this "keystone block" is removed, however, the quarrymen have operating room at the base of the layer, and successive blocks are removed by drilling short, closely-spaced holes horizontally into the base of the blocks and wedging them out with wooden pegs. When the block of stone is freed on all four sides, it is pulled over on its side, falling on piles of small stones known as "pillows" to break the impact of the fall, and cut into standard size blocks for hoisting and shipment to the mill. Work proceeds in this fashion until all the blocks on a given level are removed. The operation is then repeated for the next level down, and so forth until the base of the commercial stone is reached. Normally the standard thickness of a working level is eleven feet. In this part of the dimension stone belt the Salem is thick enough to permit six or seven levels.

(page) 21. Figure 6.

(page) 22.

Road Log
Return via quarry road to Highway 37 and turn left. Proceed southward through towns of Oolitic and Bedford. Road log will resume on south side of Bedford at Bedford Plaza shopping center.

MILEAGE

    0.0	     Bedford Plaza sign on right.

    0.1      Light gray to tan colored limestone on right.  Massive to 
             medium bedded. Fine to medium grained, oolitic.  ST. LOUIS 
             LIMESTONE.

    0.25     ST. LOUIS LIMESTONE exposed in new road cut on left and old 
             road cut on right. Notice solution features and good TERRA ROSA 
             soil on left.

    0.5      Low exposures of medium to thin bedded, blue gray ST. LOUIS 
             LIMESTONE along road to right for next 0.3 mile.

    1.0	     Begin 0.3 mile long road cut on right in tan to gray massively 
             bedded limestone at about the top of the SALEM LIMESTONE.  Old 
             road cut is on right and shows textural and structural features 
             on weathered face--styolite, and cross bedding particularly.  
             New road cut on left begins at 1.1 miles and shows solution 
             cavities.

    1.5	     Begin another long road cut in SALEM LIMESTONE.  Old 
             exposure on right.  New cut (1965) on left.  Notice solution 
             cavities and oxidation "rinds" about joint-bounded bedrock 
             blocks on left.

    2.8      Cross East Fork of the White River.  Extensive flood plain can 
             be seen to the right on the south side of the river.  The White 
             River served as a sluiceway during the Pleistocene and handled 
             great quantities of glacial outwash, aggrading its valley floor 
             to the level of the flood plain you see to the right.  Present 
             stream has incised a channel 10-15 feet deep into the flood 
             plain.

    2.9	     Exposures of medium bedded to thin bedded and argillaceous lime-
             stone, ST. LOUIS LIMESTONE, on either side of road for next 0.4 
             miles.

    3.4	     Turn right onto U.S. 50 at stop light.  Proceed westward and 
             southwestward on U.S. 50.

             From Bloomington southward to this point the road has more or 
             less parallelled the strike of the bedrock formations, crossing 
             very slightly the Mitchell plain toward the west.  As the route 
             turns westward onto U.S. 50 we cross the strike of the bedrock 
             formations and quickly work our way up the section and into the 
             Chester Series of the Crawford upland.

(page) 23.

MILEAGE

    3.6	     Sinkholes well developed on St. Louis and Ste. Genevieve lime-
             stones for next 5½ miles along U.S. 50.

    5.7	     Low exposure of light gray, medium bedded, fine grained 
             limestone. Probably STE GENEVIEVE LIMESTONE.  Wooded hills 
             to left (south) of highway are outliers of Crawford upland 
             capped with sandstone of the Chester Series.

    7.6	     Typical light gray to white, crinkly bedded STE GENEVIEVE 
             LIMESTONE in low exposure on left.  Ridge about one mile 
             ahead to west is Chester escarpment.

    8.0      Low exposure of STE GENEVIEVE LIMESTONE on left.

    8.4	     Same as above.

    8.9	     Base of Chester escarpment.  Leave Mitchell plain and ascend 
             hill through PAOLI LIMESTONE and BETHEL FORMATION (yellow-orange 
             sandstone on right).

    9.7      Interbedded black shales and olive colored sandstones.

    9.9	     Dark shale below and medium bedded to thin bedded tan to brown 
             sandstone above in road cut.  MANSFIELD (?)

   10.1      Brown to olive colored, medium to massive sandstone.  
             Mansfield (?)

   10.4	     Sandstone as before on left.  Travelling across the maturely 
             dissected surface of the Crawford upland.

   10.8	     Thin bedded black shale exposed on left.  Probably part of 
             Mansfield formation.

   11.5	     Ed's Place on left.

   11.8	     Crest of hill.  View off to west of Crawford upland surface.

   12.5	     Begin ascent into reentrant Karst Valley.

   13.2	     Low outcrop of light colored limestone on left.  Probably 
             PAOLI LIMESTONE

   13.3	     Intersection of U.S. 50 and Indiana Highway 60. Continue west 
             on U.S. 50.

   14.2	     Deep road cut on right exposes upper part of CYPRESS FORMATION
             (gray-olive shale) and BEECH CREEK LIMESTONE (massive gray 
             limestone above road on right.

             Deep cut along B & 0 main line below road and to left exposes 
             good section of Lower Chester as follows: 
                Cypress formation
                Reelsville limestone 7.0 feet
                Sample formation 22.1 feet
                Beaver Bend limestone 15.5 feet

(page) 24.

MILEAGE

   14.6	     Bridge over small stream.  Village of Huron on left.

   15.0	     Bridge over small stream.

   15.4	     Mill of the Indiana Sandstone Company on the right.  Sandstone 
             from the Elwren formation is cut and split for building and 
             decorative purposes.

   15.8	     REELSVILLE LIMESTONE on right.

   16.1	     CYPRESS FORMATION, gray shale and sandstone on right.

   17.1	     Exposure of MANSFIELD FORMATION, mostly sandstone above on 
             right.  The Mansfield lies on top of a prominent disconformity 
             at this point.  As much as 500 feet of Middle and Upper Chester 
             rocks are missing.  Considerable relief is present on the 
             pre-Pennsylvanian erosion surface that marks the disconformity.  
             A good view of the disconformity will be seen at stop 5 this 
             afternoon.

   17.9	     MANSFIELD FORMATION.

   18.1	     MANSFIELD FORMATION.

   18.4	     MANSFIELD FORMATION.

   18.8	     MANSFIELD FORMATION.

   19.0	     MANSFIELD FORMATION.  Extensive exposure of Mansfield across 
             valley to south.  Note irregular base of sandstone member.

   19.4	     Entrance to Martin State Forest on right, Indiana Highway 650 
             to the left.  LAST THREE CARRYALLS TURN LEFT ONTO highway 650 
             AND PROCEED TO U.S. GYPSUM MINE.  First three carryalls 
             continue straight ahead on U.S. 50.
----------------------------------------------------------------------------
ROAD LOG FOR GROUP GOING TO U.S. GYPSUM MINE.

   19.4	     Turn left onto Indiana 650.

   19.7	     Road cut in MANSFIELD FORMATION, close to unconformity.

   20.1	     Deep road cut in Chester Series which exposes 25' of the
             CYPRESS FORMATION, the BEECH CREEK LIMESTONE, 15', and 25' of 
             the BIG CLIFTY SANDSTONE.

             The Beech Creek limestone is perhaps the most easily recognized 
             limestone in the Chester Series, partly because of its dark 
             gray, fine-grained, gastropod-bearing character in the lower 
             part, but also because of large crinoid stems (up to 1 inch in 
             diameter) in the upper part.

(page) 25.

MILEAGE

             The Big Clifty sandstone, unlike most of the clastic units in 
             the Chester, maintains a remarkably constant lithology, appearing 
             almost everywhere as an even-bedded, frequently laminated, fine-
             grained, well sorted, quartzose sandstone.

   20.3	     At base of hill turn right and proceed westward and 
             southwestward around artificial lake to office of U.S. Gypsum 
             Mine.  Stop 3.
-----------------------------------------------------------------------------

   19.9	     MANSFIELD FORMATION.

   20.0	     MANSFIELD FORMATION.

   20.3	     Cross broad flood plain of Beaver Creek.  Small knoll in middle 
             of flood plain is circumalluviated bedrock hill underlain at 
             surface by BEECH CREEK LIMESTONE.

   20.7	     BEECH CREEK LIMESTONE exposed along road on left.  Overlain by 
             dark gray siltstone and sandstone of BIG CLIFTY FORMATION.

   20.9      MANSFIELD FORMATION.

   21.0      MANSFIELD FORMATION.

   21.5	     Turn left into National Gypsum Company plant.  Stop 3.
U.S. and National Gypsum Company Mines

Stratigraphy. -- An account of the stratigraphy of the gypsum and associated strata is taken from French (1965, p. 2-4). See also figure 7.

The lower part of the St. Louis limestone in the evaporite section of southwestern Indiana is largely composed of brown carbonaceous limestones alternating with gypsum and anhydrite. Black, gray, red, and green shales are found near the top of the unit. Dolomite is present in tan to brown fine-grained strata that are locally continuous and in lenses associated with minor structural highs. Traces of chlorides have been found within the evaporite zone. Fluorite crystals are present in vuggy carbonate rock above and below the evaporite unit. Argillaceous laminae from within the lower St. Louis were examined by Harrison and Droste (1960), who found the partings to be composed of dolomite, gypsum, quartz, illite, chlorite, and mixed-layer illite-montmorillonite.

The evaporites occur in four or fewer beds, none of which is known to exceed 16 feet in thickness. Limestone and dolomite of varying thicknesses separate the evaporite beds, and a very thin shale is locally present immediately above the gypsum or anhydrite. Most of the gypsum is gray to white and is largely recrystallized in the tabular selenite form. Some pink to brown selenite is locally present near the top of the unit. Secondary gypsum, that has recrystallized in near-vertical fractures and along bedding planes is mostly of the fibrous "satin spar" variety. This

(page) 26. Figure 7.

(page) 27.

secondary material is white to transparent and in places contains inclusions of shale or carbonate rock that have been displaced from the surrounding material. Blue-gray anhydrite is found in both lateral and vertical continuity with the gypsum. Inclusions of dolomite are common within the anhydrite, and conversely, anhydrite veins and crystals are commonly found in the dolomite. Bundy (1956) stated that much of the anhydrite was re-crystallized from older anhydrite or gypsum.

Examination of cores and the ore body in both of the mines at Shoals indicates that the commercial deposit was not precipitated as a single continuous unit. Thin dolomites that can be traced over many acres and thick irregular masses of partly replaced dolomite lie within the main ore body. But the upper and lower contacts of the major evaporite zone appear to be relatively smooth or only slightly undulating. This suggests that, whatever the amount of carbonate rock replacement that has taken place since the original deposition, the diagenesis has been contained within reasonably well-defined upper and lower boundaries. The extent of replacement may have been limited vertically by thin but impermeable argillaceous zones.

The St. Louis Limestone is exposed at the surface a few miles east of the major evaporite beds but only traces of nodular gypsum have been noted in the outcrop area. Breccia within the section suggests that the gypsum, if formerly present, may have been leached by percolating ground water. A similar situation is present in Illinois where Saxby and Lamar (1957) have recorded the presence of breccia and the absence of gypsum in the outcrops.

According to Bundy (1957) the initial evaporite deposit in southwestern Indiana was probably gypsum. Subsequent burial of the deposits converted the gypsum to anhydrite. The present deposits of commercial gypsum are derived through rehydration of the secondary anhydrite by ground water. This rehydration appears to predominate along the structurally high eastern flank of the deposit where the evaporites are generally less than 500 feet from the surface. The reintroduction of water into the evaporite zone has not been confined to any certain level, however, because gypsum is found more than 1,100 feet below the surface, and anhydrite is found above 500 feet. Saxby and Lamar (1957) recorded gypsum in Illinois at a maximum depth 1,500 feet below the surface, and anhydrite at a minimum depth of 560 feet below the surface. The abrupt termination of the main gypsum bed on the eastern flank of the Indiana deposit and the presence of breccia within the evaporite zone indicate that in some areas the position of the eastern edge may be the result of leaching rather than non-deposition.

Depositional Environment. -- It is generally accepted that a restricted environment in which the normal marine circulation has been modified by a sill or barrier is required for the deposition of gypsum. The mechanics of developing such an environment may vary considerably and are not fully understood with respect to the evaporites of southwestern Indiana. McGregor (1954) postulated that epeirogenic movements periodically caused sills to form within the basin. Pinsak (1957) suggested that the sills were caused by progressively formed structures in the strata overlying Silurian reefs.

(page) 28.

Mining Operations (U.S. Gypsum Company Mine). -- The gypsum bed at the U.S. Gypsum Company mine is reached by a 430 foot vertical shaft. The mine employs the room and pillar method with 25-foot-wide rooms and 30-foot-wide pillars. Three Joy CD-42 double boom-mounted 1¾ inch drills are used to drill the gypsum. Ammonium nitrate and regular blasting caps are used to blast the ore, with each shot averaging about 200 tons. After blasting the ore is loaded into 10 ton capacity LeTourneau or 15 ton capacity Wagner telescoping trucks and transported to the primary crusher. The ore is reduced to minus 8-inch size in the primary crusher (a 3Ox48 inch single roll, 200 tons-per-hour capacity) and hoisted to the surface in skips which discharge the ore into hoppers for secondary crushing. A double-roll crusher reduces the ore to minus 3 inches and a 3-foot gyratory crusher reduces the ore to about 1 inch before final grinding. Three roller mills then grind 95% of the ore to minus 100 mesh.

Over 100 wallboard and plaster products are manufactured at the plant, raw gypsum is also marketed for portland cement, agricultural uses, and glass manufacture.

Mining Operations (National Gypsum Company Mine). -- The gypsum bed at the National Gypsum Company mine is reached by means of a 1,986 foot long inclined shaft that descends from the surface at an angle of 17½° to a vertical depth of 550 feet. The gypsum bed averages 14 feet in thickness at the mine, and it is removed via the room and pillar method. The working face is drilled with two boom-mounted CD-42 carbide steel bits 1 ¾ inches in diameter, and 12 feet, 11 inches long. The ore is blasted, using ammonium nitrate and electric time-delay caps and 1 ½" x 6" sticks of high-velocity dynamite as primers. It is then trucked to the primary crusher at the base of the inclined shaft and brought to the surface on a 30-inch-wide conveyer belt.

The ore is crushed further and ground at the mill. Daily production averages 1,600 tons. Nearly 800 tons of fines (minus 1/4-inch) are calcined each day for use in the board plant and plaster mill, which produces 24 types of wallboard and nearly a quarter billion board feet annually. About 500 tons of cement (retarder) rock is produced daily for rail shipment to various cement plants in the midwest. Anhydrite also is furnished to cement companies at a rate of about 50,000 tons annually.

(page) 29.

Road Log
Return to U.S. 50 and continue westward into Shoals. Road log resumes in Shoals at Bridge over White River.

MILEAGE

    0.0	     Bridge over East Fork of White River.  The town derives its 
             name from the shoals of the White River, about 100 yards 
             downstream (left) of the bridge where the basal sandstone member 
             of the Mansfield formation forms a temporary base level for the 
             stream.

             The shoals mark the position of a pre-Mansfield valley because 
             rocks of the Chester Series outcrop both north and south of 
             this location at higher altitudes.  Crossbedding in the Mansfield 
             formation (Pettijohn, Potter, and Siever, 1965, p. 164) is 
             oriented to the southwest.

    0.6	     Deep road cut in MANSFIELD FORMATION.  Orange-brown, massively 
             bedded sandstone.  Crossbedded in lower part of exposure.

             At end of cut on right look down into woods for view of 
             pedestal rock--an interesting erosional remnant in the Mansfield.

    1.3	     MANSFIELD FORMATION on right.  Good view of White River valley 
             on left.

    1.6	     Start down long grade.  Exposures of MANSFIELD FORMATION on 
             left.  Note excellent crossbedding at 1.9 and 2.0 (on right).

    2.9	     MANSFIELD on right.

    3.4	     Deep road cut on right in MANSFIELD FORMATION.  Sandstone 
             (40') on top, black shale and olive-colored, thin-bedded 
             siltstones in middle (20'), and massive brown to olive drab 
             sandstone at base of exposure.  Base of upper sandstone cuts 
             down through shale and siltstone at western edge of roadcut.

    3.7	     Start up hill with exposures of MANSFIELD FORMATION on right.  
             Note varied lithologies, including thin shaly coals.

    5.8	     Sand and gravel pit on right in Illinoisan outwash terrace.  
             Heavy sand and loess cover on slope to northeast.  Possibly 
             Wisconsin material.

    6.2	     Cross bridge over Boggs Creek.  MANSFIELD sandstone in cut on 
             west side of bridge.

    7.5	     Enter Loogootee.  Continue westward on U.S. 50 to intersection 
             with U.S. 231.  Turn right onto 231 and proceed north out of 
             town.  Road log resumes at stop light in Bloomfield 24 miles to 
             the north.
(page) 30.

MILEAGE

             From Loogootee to Bloomfield the route is along the transition 
             between the lower Wabash lowland to the left and the rugged 
             Crawford upland to the east.  For about the first twelve miles 
             north of Loogootee the road is at an altitude near the base of 
             the Brazil formation.  The larger stream valleys close to 
             Bloomfield cut down into the Mansfield.

CHECK MILEAGE
    0.0	     Stop light in Bloomfield.  Turn left with U.S. 231 and 
             Indiana 54 and proceed westward.

    0.6	     Leave Bloomfield and start across flood plain of West Fork of 
             White River.

    1.5	     Bridge over West Fork White River.

    4.0	     Intersection of 231-54 and 57.  Continue straight ahead 
             (westward) on State Highway 54.

    5.0	     Spoils piles on right at top of small rise from coal strippings.
             LOWER BLOCK COAL near base of BRAZIL FORMATION.  Coal is about 
             2 feet thick.

    6.1	     Enter Switz City.

    6.5	     Intersection of Highways 67 and 54.  Continue straight ahead 
             (westward) on 54.

   11.7	     Linton city limits.  Continue on Highway 54 through Linton to 
             lunch stop. 

   14.3      Klusmeiers Drive In Restaurant.  LUNCH.
Continue northward and westward on Highway 54 for 7.3 miles through Dugger out to Livingston's grocery store and Gulf Service Station. Turn right onto county road and proceed northward to Minnehaha Mine. Stop 4.

Minnehaha Mine, Dugger, Indiana
Contributed by Charles E. Wier
Stratigraphy. -- The Minnehaha Mine is one of 14 large coal-producing strip mining operations in Indiana. Last year it produced more than a million tons of coal. Probably it will exceed one and a half million tons in 1966. Most of the coal produced comes from a seam called Coal VI by the miners, although some production comes from Coal VII which is 45 feet above Coal VI.

Coal seams were designated by Roman numerals before 1900 by G. H. Ashley who made the first comprehensive survey of Indiana coal deposits. Thus the number does not indicate quality or quantity but indicates the general position of the coal. Nearly all the production in Indiana comes from Coals III, IV,

(page) 31.

V, VI, and VII (named from bottom to top). Below Coal III are coals of less economic importance called Minshall, Upper Block and Lower Block coals. The coals dip southwestward 20 to 30 feet per mile. Thus the younger coals are mined by stripping to the east. The strip mining near Switz City is in the two Block coals, that near Linton in Coals III and IV, between Linton and Dugger, Coals V and VI, and in the vicinity of Dugger, Coals VI and VII.

Coal VI is in the Dugger Formation and is well developed in the Dugger area. It ranges from 5 to 8 feet in thickness, averaging 6 feet. It is characterized by three shale and pyrite partings that are less than one inch thick. The upper two are about 8 inches apart. They occur in the upper third of the coal seam and are present in Coal VI everywhere it is exposed in Sullivan County. Above Coal VI is 30 feet of light gray, thin-bedded, micaceous shale and a tan, massive- to thin-bedded, fine-grained sandstone. Locally this interval is entirely sandstone and in some places Coal VI is absent and this sandstone fills its position. In the Dugger area the Universal limestone commonly is not present above the clastic sequence, but its position is indicated by calcareous sandstone that contains small buff limestone nodules. Above this zone is 10 feet of gray sandy shale and the underclay of Coal VII. Coal VII ranges from 2 to 4 feet in thickness and is, in general, more friable and thinner banded than Coal VI, and it is slightly lower in sulphur and in B.t.u. value. Coals VI and VII are typically bright banded, high volatile C bituminous coals.

Coal VII is the top member of the Dugger Formation. Thus, the overlying shale and sandstone is in the basal part of the Shelburn Formation. The roof of Coal VII is gray, thin-bedded, sandy shale that ranges from 1 to 20 feet in thickness and contains bands of sideritic nodules and, locally contains abundant plant fossils both in the nodules and as carbonized imprints in the shale. This shale is overlain by the Busseron sandstone.

Mining Operation. -- Before the coal can be obtained in a strip mine, the dirt and rocks above the coal must be removed. To do this job Ayrshire installed a new dragline, which is designated as the Bucyrus-Erie Model 2550-W dragline. This giant swings a 75 cubic-yard bucket from a 275-foot boom, and is able to fill the bucket with 110 tons of rock at a depth of 165 feet below its own level, hoist this 100 feet above its base and dump it 500 feet away, then swing back ready to fill the bucket again -- all in less than one minute.

The 2550 dragline generates 17,000 h.p. from its 20 motors which use 6900 volts of 3-phase 60-cycle electricity purchased from Public Service Company of Indiana. The coal produced from the mine is used to help generate this electricity.

Although the dragline cost more than $6 million it will, with its increased efficiency, enable the company to better compete in the fuels market. It also will allow them to mine coal at greater depths than at the Friar Tuck Mine.

After the overburden is removed, a loading shovel fills 50-ton trucks which haul it over a company-owned road to the preparation plant. This plant, used until recently by the Minnehaha underground mine, cleans some of the ash and sulphur from the coal.

(page) 31a.

After the coal is removed from the ground, Indiana State law requires that the land be reclaimed in such a manner that the value of the land will be enhanced; that soil erosion, hazards of floods, and the pollution of water will be reduced; and that, where possible, wildlife will be encouraged and protected. Normally this means constructing earth dams in final cuts in order to impound the water, knocking the tops off the strip-mine ridges and peaks, and planting the area in trees. Seedlings are planted at a density of about 700 per acre. Conifers are commonly planted, but hardwoods are planted where the pH of the strip mine spoil is high enough.

Probably the first strip mine reclamation project in the United States was to the northeast in Clay County, Indiana, where, in 1918, several acres of spoil were planted in fruit trees. Some of these still bear fruit. As early as 1926 member companies of the Indiana Coal Producers Association began a voluntary but limited reclamation program, but before the State's reclamation law was passed in 1941, most of the strip mined area was simply abandoned. Since 1941, however, nearly all of the approximately 2000 acres stripped each year in Indiana are reclaimed. Some of the reclamation work is minimal and leaves much to be desired.

About 75 percent of the 85,000 acres disturbed by strip mining of coal in Indiana has been planted in trees. Only 20 percent of the stripped area has been graded and seeded and is now utilized as farms. Another 6 percent has been seeded but not graded. Because more than 10 percent of the strip mined area is left as lakes, some areas are ideal for development for recreational uses.

Trees planted on strip mine spoil in this area include locust, Scotch pine, jack pine, oak, maple, cottonwood, sycamore, European alder, and walnut. Some of the abandoned strip mines, such as those north of Highway 54 east of Linton, are so well covered by trees that one cannot recognize them as mined areas. In contrast, the recently mined areas either have not yet been planted or the seedlings are only a foot or two high.

(page) 32.

Road Log
Return southward along county road to Highway 54. Turn left and retrace route eastward to Bloomfield. Road log resumes in Bloomfield at traffic light.

CHECK MILEAGE.

MILEAGE

    0.0	    Traffic light in Bloomfield at intersection of 231-54 and 157.  
            Continue straight ahead (eastward) on 54.

    1.6	    Cross Richland Creek.  Note extensive flood plain.  Begin ascent 
            onto Crawford upland.

    3.3     MANSFIELD FORMATION (sandstone) exposed in slope to right of 
            road.

    3.6	    Blue Barn at curve on right.

    5.4	    Turn left off 54 onto county road.  Be careful.  Heavy traffic.

    5.5	    Bear right and start down steep hill.

    6.0	    Exposure of cross-bedded, massive sandstone in valley wall to 
            right.  Mansfield(?) Big Clifty(?)

    7.2	    Bear left.

    8.2	    Bridge over Illinois Central Railroad.  Stop 5. Park cars on 
            South side of bridge and walk along south side of deep railroad 
            cut.
(page) 33.

Illinois Central Railroad Cut, Solsberry, Indiana
The north wall of the Illinois Central Railroad cut exposes perhaps the most significant unconformity in the Paleozoic rocks of the midwest. See figure 8 below. About 400 feet of the Upper Mississippian is missing at this locality and its place is taken by an old erosion surface-marked by a thin layer of porous iron ore.

The trace of the unconformity on the north wall of the railroad cut outlines part of the east wall of a pre-Mansfield valley. The unconformity dips below track level near the railroad bridge so that the floor of the old valley is hidden from view. The unconformity itself has a decidedly step-like character and reflects old bedrock benches or terraces controlled by the variable lithologies of the Golconda and Big Clifty formations. These "bench makers" have been utilized also by the railroad in maintaining what has been a troublesome cut, subject to numerous slumps and rock falls.

About one-third of the way up on both sides of the cut is a prominent bench whose surface is the top of the Golconda limestone, a marine limestone containing numerous ARCHIMEDES, FENESTELLA, PENTREMITES, and several species of brachiopods, rugose corals, and crinoid columnals.

Shale, underclay, coal, siltstone, and sandstone of the Mansfield formation overlie the unconformity. The thin coal exposed near the railroad bridge and extending several hundred feet to the east is probably a flood plain swamp deposit formed during filling of the pre-Mansfield valley. Other indications of plant life and a continental or deltaic environment of deposition for the Mansfield formation are LEPIDODENDRON and SIGILLAREA impressions in shales, siltstones, and sandstones, and cephalopod and gastropod-like molds (marine?) in some of the coarse reddish-brown sandstones from the base.

Basal beds of the Mansfield formation overlie formations ranging from the New Albany shale of Late Devonian age to the Kinkaid limestone of Late Mississippian age. The unconformity is more or less continuously exposed from the Ohio River northward to the Pleistocene overlap north of Crawfordsville. From south to north the unconformity cuts downward into progressively older rocks.

Figure 8.

(page) 34.

Relief on the unconformity varies greatly but ranges from about 50 to 150 feet. The exact position of the unconformity is difficult to pick, not only because the surface is irregular, but also because most of the major rock types characteristic of the Mansfield are common to the underlying rocks as well.

Gray (1962) considers the Mansfield to have a depositional environment possibly similar to that of the present delta of the Rio Grande River. Siever (1951) believed the unconformity had two stages of development; widespread regional truncation of underlying rocks followed by rejuvenation which produced sharply entrenched erosional valleys. This valley system trends southwestward in most of the Illinois Basin, particularly the eastern half in Indiana.

(page) 35.

Road Log
Road log resumes on north side of bridge across Illinois Central Railroad track.

MILELAGE

    0.0	    North side of bridge.

    0.2	    Bear right.

    1.0	    GOLCONDA LIMESTONE in low exposure on left.

    3.1     Road crosses bridge over deep railroad cut along Illinois 
            Central.  Sandstone exposed in cut probably MANSFIELD.

    3.9	    Village of Solsberry.  Continue straight ahead on Indiana 43 
            after stop at intersection.

    4.4	    Dangerous underpass.

    4.9	    Indiana 43 bears left. STAY STRAIGHT AHEAD (eastward) on county 
            road.

    6.6	    Bridge over Illinois Central track.  Deep cut in massive 
            sandstone west of bridge and also to east.  Probably MANSFIELD.

    7.5	    Cross narrow valley along county road for 0.9 mile to 
            intersection with State Road 45.  Sandstone ledges exposed along 
            valley walls. BIG CLIFTY (?)

    8.4	    Intersection of county road with State Road 45.  Turn left.  
            Enter Monroe County.

    8.7	    Start down Chester escarpment at eastern edge of Crawford upland.

    9.3	    Village of Stanford.  Road climbs over outlier of Crawford upland.

   l0.4     Back into Mitchell plain.

   10.5	    STE. GENEVIEVE LIMESTONE on right.  Notice prominent sinkholes
            on either side of road.  Wooded hills to right (south) are 
            outliers of Crawford upland.  Road follows large karst reentrant 
            into upland.

   14.6	    Sinking stream in pasture on left.

   16.4	    Twin Lakes.  Early and unsuccessful attempt to impound surface 
            water for municipal water supply.

   17.4	    Abandoned stone quarry on left in ST. LOUIS LIMESTONE.

   17.7	    Bloomington city limits.  Proceed on 45 (West Second Street) to 
            the third traffic light.  Turn left onto South Walnut Street and 
            drive north through town to the sixth traffic light.  Turn right 
            onto Tenth Street and proceed to Geology Building.

   20.0      Geology Building.
(page) 36.

References Cited
Beede, J. W., 1910, The cycle of subterranean drainage as illustrated in the Bloomington, Ind., quadrangle: Indiana Acad. Sci. Proc., v. 20, p. 81-111.

Bundy, W. M., 1956, Petrology of gypsum anhydrite deposits in southwestern Indiana: Journal of Sed. Petrology, v. 26, p. 240-252.

French, R. R., 1965, Geology of gypsum and anhydrite in southwestern Indiana: A.I.M.E. Ann. Meeting, 1965, 14 p.

Gray, H H., and others, 1960, Geology of the Huron area south-central Indiana: Indiana Geol. Survey Bull. 20, 78 p.

Gray, H. H., 1962, Outcrop features of the Mansfield Formation in southwestern Indiana: Indiana Geol. Survey Rept. Prog. 26, 40 p.

Harrison, J. L., and Droste, J. B., 1960, Clay partings in gypsum deposits in southwestern Indiana: 7th Natl. Conf. on Clays and Clay Minerals, p. 195-199.

Malott, C. A., 1922, The physiography of Indiana, in: Handbook of Indiana Geology, Indiana Dept. Cons. Publ. 21, p. 59-256.

McGregor, D. J., 1954, Gypsum and anhydrite deposits in southwestern Indiana: Indiana Geol. Survey Rept. Prog. 8, 24 p.

Perry, T. G., Smith, N. M., and Wayne, W. J., 1954, Salem limestone and associated formations in south-central Indiana: Indiana Geol. Survey, Field Conf. Guidebook, No. 7, 73 p.

Perry, T. G., and Smith, N. M., 1958, The Meramec-Chester and intra-Chester boundaries and associated strata in Indiana: Indiana Geol. Survey Bull., 12, 110 p.

Pettijohn, F. J., Potter, P. E., and Siever, R., 1965, Geology of Sand and Sandstone: Indiana University, 208 p.

Pinsak, A. P., 1957, Subsurface stratigraphy of the Salem Limestone and associated formations in Indiana: Indiana Geol. Survey Bull. 11, 60 p.

Saxby, D. B., and Lamar, J. E., 1957, Gypsum and anhydrite in Illinois: Illinois State Geol. Survey Circular 226, 26 p.

Siever, Raymond, 1951, The Mississippian-Pennsylvanian unconformity in southern Illinois: Am. Assoc. Petroleum Geologists Bull., v. 35, p. 542-581.

Winslow, J. D., Gates, G.R., and Melhorn, W. N., 1960, Engineering geology of dam site and spillway areas for the Monroe Reservoir, Southern Indiana: Indiana Geol. Surv. Rept. of Progress No. 19, 19 p.

[End]
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