MAP DETAIL from
"Map Showing the Thickness and Character of Quaternary Sediments in the Glaciated United States East of the Rocky Mountains"
U.S. Geological Survey Miscellaneous Investigations Series Map I-1970
1993-1998
by David R. Soller
The glaciers scoured the landscape and, where they flowed over relatively weaker bedrock, deep valleys were carved. In the many places where river valleys existed before the glaciers, they were extensively modified and deepened. These two images show valleys in northwestern Pennsylvania, near Erie, which are filled by thick glacial sediment. These sediments are, in many places, excellent sources of groundwater. Also shown are thin glacial sediment on the valley uplands, and the terminus of the glacier, to the southeast (lower right).
