Hydrology of the Martinsburg Formation in Lehigh and Northampton Counties, Pennsylvania

The Martinsburg Formation underlies the northern half of Lehigh and Northampton Counties, and is of Middle and LateOrdovician age. It is bounded on the south by older Ordovician limestone formations and on the north by a ridge-forming conglomerate of Silurian age. Recent mapping has supported a three-part division of the Martinsburg into a lower thin-bedded slate {Bushkill Member), a middle graywacke-bearing unit (Ramseyburg Member), and an upper thick-bedded slate (Pen Argyl Member).