1. Altitude and configuration of the potentiometric surface in the Triassic sandstones and shales, northern Chester County, Pennsylvania, October 1989 through March 1990 Yale Public content 1990. 2002-06-01T04:00:00Z. 2002-06-01T04:00:00Z. Geological Survey (U.S.). The Survey. English. Public. Pennsylvania and Chester County.