The diagram below is a generalized geologic map of Pennsylvania, modified from Map 7 of the Pennsylvania Geologic Survey. The green circle represents the location of Bucknell University, in Union County. 

The geology of Pennsylvania may be subdivided into three broad categories:

  1. Flat to gently folded strata of the western and northern portions of the state. These sedimentary rocks were deposited from 400 to 250 million years before present and contain a vast resource of bituminous coal;
  2. Moderately to tightly folded strata of central Pennsylvania. These sedimentary rocks were deposited from 570 to 290 million years ago and contain valuable reserves of anthracite coal.
  3. Metamorphic and igneous rocks of southeastern Pennsylvania. These rocks record a complex history of mountain building and opening of the present day Atlantic Ocean. They range in age from nearly 1 billion years to 140 million years before present.