Brief outline of Pennsylvania’s Geologic History
Kurt Friehauf
405-360 million years ago – Devonian Acadian-Caledonian Orogeny
Although it didn’t greatly affect Pennsylvania, another island arc did accrete onto (smash into) the continent further north. Maine and the Maritime Provinces of Canada were much more strongly affected. The collision also may not have been “head-on” either, rather it may have been more of a glancing blow to the continent. In any case, we do see another angular unconformity in which Devonian-and-older rocks were tilted, eroded, and subsequently buried beneath new sediments.
