When visiting rock and fossil shows or shops I always keep and eye out for items from Pennsylvania. Swatara Gap material especially so since that is a now closed site and I only collected there once or twice as a child.
This plate caught my eye because of the large, detailed Rafinesquina brachiopod. It is preserved in a very fine grained sandstone (or sandy mudstone).
Here is another that I collected years ago from the site.
Swatara Gap was a well known collecting site up until about ten years
ago when the Pennsylvania Department of Transportation buried the site
to prevent undercutting of I-81. The Martinsburg formation is dated to
the late Ordovician (Katian stage or Tentonian to Edenian of N. America