There still exists some uncertainty as to the limitation of several of these rock-groups, and though much advance has been made by the study of them in different parts of the state, many difficulties constantly arise in the way of correlation. In this report it has been thought best to group the formations and color them on the map as they would appear to the ordinary field observer without doing violence to any particular system of nomenclature, and mainly with a view of graphically representing the econonomical features.
The Catskill Rocks. No. IX.
This formation, which is colored a pinkish-red on the map, only exists in Snyder county, occupying the troughs of the two main synclinal basins. Only a portion of the formation has been preserved there, the greatest thickness of rocks showing along the Susquehanna river opposite Northumberland, in all about 3500′ thick, including about 1000′ of the “Transition Rocks” at the base.
Some geologists prefer to separate this lower group, having fossil types common to both the Catskill and Chemung formations; but it will suffice to know that they have been included here in the Catskill, whose base has been fixed at the lowest red bed, for no other red beds are seen until we descend the geological column to No. Vc, the lower Salina rocks. These red beds therefore seem to offer a fairly good lithological division between No. IX and No. VIII, and the map has been colored accordingly.
The Catskill rocks, so considered, show in Snyder county an upper series of red sandstone and shales, with some few greenish-gray beds, in all about 2500′ thick and well exposed in the cuts of the Sunbury, Lewisburg and Williamsport (P. and R.) railroad, on the west side of the river opposite Northumberland. The bottom portion of the formation, 1000′ thick, whose red beds are not so prominent and have a less vivid hue, contain much olive-green shale and brownish-red sandstone. These rocks are well exposed along the public road from Northumberland to Shamokin Dam, and
