But the mantle is not solid. It’s moving slowly, and the continents are simply thin layers
of crust that float on top of the mantle. They move about as convection currents within
the mantle push them this way and that. They tilt and rock from side to side.
Events within the mantle periodically push magma upwards into the crust. Sometimes the
magma reaches the surface and erupts as volcanoes. Sometimes it pushes upward but does
not reach the surface. The intrusion of magma deforms the overlying rock layers. When
the magma cools slowly, it forms granite.
To follow the next events, we need to expand our view to the west, and look at a wider
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