county, owing to greater erosion and concealment; but the above fairly represents the character of the formation, typically developed. Varying sections of these rocks of No. VIII may be seen on Mahantango creek in southern Snyder, and along Penns creek and upper Middle creek between Jack’s and Shade mountains. Their exposed thickness decreases somewhat going west from the river, owing to erosion and the western rise of the Northumberland synclinal, so that in Spring and West Beaver townships nearly the whole valley between the two Oriskany sandstone ridges is occupied by the black Marcellus slate, and Hamilton, here largely shale, and perhaps some Genessee beds.
The Marcellus black slate has been a very fruitful source of disaster to many coal mining companies throughout the district, which have labored long and earnestly to find coal in them. Every effort has proved a failure, as well as similar operations in the Hudson River and Utica slate formations No. III.
Union county contains only a very small amount of the No. VIII formation, caught in the Buffalo valley synclinal north of Lewisburg, where perhaps the whole of the Marcellus formation exists, but little if any of the overlying Hamilton.
Mifflin county contains a fair section through the Lewistown valley of Marcellus and Hamilton rocks, and the Portage group is especially well developed in Wayne township along the Juniata river. There does not appear to be any representation of the Chemung rocks at all in this county, so that those portions of the Lewistown valley occupied by the rocks of No. VIII present a very different topographical aspect to land so occupied in Snyder county.
The valley between Jack’s and Shade mountains, which is deep enough along the Susquehanna to contain Catskill rocks No. IX, shoals up rapidly, until in Decatur township of Mifflin county the Chemung group is entirely wanting; the Portage is represented by a series of thin flags and sandy shales, making a sharp synclinal (double) ridge along the center of the valley; the Genesee and Hamilton slates, shales and sandstones making valleys on either side of the
