An Introduction to Plate Tectonics
Continental drift-Rock Sequences
Rock sequences in South America, Africa, India, Antarctica, and Australia show
remarkable similarities. Wegener showed that the same three layers occur at each of
these localities. The bottom (oldest) layer is called tillite and is thought to be a
glacial deposit. The middle layer is composed of sandstone, shale, and coal beds.
Glossopteris fossils are in the bottom and middle layers. The top (youngest) layer is
lava flows. The same three layers are in the same order in areas now separated by
great distances. Wegener proposed that the rock layers were made when all the
continents were part of Pangaea. Thus, they formed in a smaller contiguous area that
was later broken and drifted apart.
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