Yep - a result of a series of orogenies (most notably the Taconic, Acadian and Alleghanian) resulting from North America and other continents colliding.
Hate to cite wikipedia, but these cover it pretty well.
Geology of the Appalachians - Wikipedia, the free encyclopedia
Alleghanian orogeny - Wikipedia, the free encyclopedia
Acadian orogeny - Wikipedia, the free encyclopedia
Taconic orogeny - Wikipedia, the free encyclopedia
Driving through Pennsylvania - take a look at the rock cuts along the roadside. Going from southeast to northwest - you'll see the rocks are tilted and deformed due to the continental collision. Continuing west, the deformation will decrease until the bedding will be nearly horizontal.
If you have a long car trip through PA (or just want to bore your kids, as I often do) - check out the Roadside Geology series.
http://www.amazon.com/Roadside-Geology-Pennsylvania/dp/0878422277