Pennsylvania Geology: Precambrian Rocks in the Reading Prong

(Dave Kline recently had a piece in the Reading Eagle about a Precambrian rock he found next to the Schuylkill, check it out here.)

I'd written before about the very early Jurassic igneous rocks on some of the small but steep hills in central-to-southeastern Berks (the Jacksonwald Outliers.) Here is a map of the rock in Berks showing that clearly in red, as well as the Precambrian age of South Mountain and the Reading Prong. South Mountain is the "front range" of the Appalachians until it kind of dies just before getting to the Susquehanna, as the Appalachians are making their turn to the east, and in Berks they're basically the hill that Galen Hall is on, as well as the hills in Spring and Cumru Townships, before rising again as Mount Penn Neversink and continuing east-northeast.

Original PDF is here but I've shrunk it to a graphic file. Red is Jurassic, green is Precambrian.