Shape files are used to display geologic units on a map. One example is Google Earth Pro, which you can load shape files into directly. Depending on the size of the data set, these files can slow the programs down. For example, the Pennsylvania set takes almost two minutes to load and display.
Pennsylvania Shape Files can be downloaded from USGS.
There is a good service online available to see the base shape files. Mapshaper is a tool for viewing and simplifying shape data. It can read in shape files, GeoJSON and TopoJSON. It can export the same formats. Using the simplification tools, shapes can be trimmed down for smaller file sizes. You can also use the console on the tool to filter individual layers out.
Shape File Links for PA and OH
The Casselman Formation
As discussed on this website, the Casselman Formation or Glenshaw Formation is a good indicator for where to find Ames Limestone. To find the location of the Ames Limestone, you only need to find the Glenshaw/Casselman boundary. I filtered data from Pennsylvania shape files and converted it to KML data. Once I had that data, I was able to embed it into a custom Google Map. This is helpful as you can view the formation while out in the field on your phone.
ArcGIS Online map of the Pennsylvania Data