On the left is a photograph of Muir Glacier taken on August 13, 1941, by glaciologist William O. Field; on the right, a photograph taken from the same vantage on August 31, 2004, by geologist Bruce F. Molnia of the United States Geological Survey (USGS).
On the top is a photograph of McCall Glacier from July of 1958 taken by Austin S. Post; on the bottom, a photograph taken from the same vantage on August 13, 2003 by Matt Nolan.
Rock sequences in South America , Africa , India , Antarctica , and Australia show similarities. Wegener showed that the same three layers occur at each of these places. 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 said that the rock layers were made when all the continents were part of Pangaea. Thus, they would have to have been formed in an area that was later broken and drifted apart.