Evidence of the location of global climatic belts is found in locations where the climate is currently different.
Large continental glaciers can only grow over continents in frigid regions of the planet, today near the north and south poles. Glaciers cannot grow over the oceans, which are too warm and melt the ice. Rocks caught on the bottom of glaciers create grooves in the rock beneath as they flow across the land. These grooves point in the direction the glacier went.
If the continents had always been in the same position then late Paleozoic glaciers grew much closer to the equator than is possible today and grew over the oceans. Wegener thought the more reasonable explanation was that the glaciers flowed on the supercontinent Pangaea and that the supercontinent was nearer to the South Pole than the individual continents are today.
Coal forms in lush tropical regions where a multitude of plants grow and die. Coal seams dating from the upper Paleozoic are found in regions that are currently much too cool. Wegener saw this as more evidence that the continents were once joined.