The drive along U. S. Route 55 from Riverton to Strasburg, Va., thence southward on U. S. Route 11 to New Market reveals striking examples of very steep, thinly wooded shale slopes extending more or less interruptedly many miles along the west slopes of the Massanutten ridges, comprising the Martinsburg shales of the Ordovician period. These shales are of wide extent and occur southward far beyond the Massanutten ridges, and westward into the Alleghenies, where other strands and outcrops appear.