1 
; k 
958 The Materials of the Appalachians. [Nor 
` The Catskill-Pocono Conglomerate, Upper Devonian and Lower 
Carboniferous. 7 
The Oriskany Sandstone, Lower Devonian. nn 
The Medina Sandstone, Middle Silurian. 4 
All these vary much in thickness in different places, butal 
are thickest and heaviest and contain the largest pebbles in the 
eastern or southeastern part of the district, and all thin out, 
more or less, towards the northwest. To assign to them a 
average thickness that would satisfy every one is, probably, im- 
possible, but the following attempt will be exact enough for my 
present purpose. No doubt can be entertained of their original 
extension over the whole Appalachian area, though all four have 
since been largely eroded. a 
The Medina, with the Oneida, maintains its mass over most 
of its exposures in the State, showing less diminution westward 
than some of the other strata. It is two thousand feet deep i 
the Kittatinny, and more than that in the Bald Eagle Range; 
so that an average of one thousand feet may be safely assumed 
The Oriskany is the thinnest of the four, but its extent is 
less than that of the others. In some places it reaches thre? 
hundred feet in thickness, but is usually much less. It may be 
therefore thrown out of our estimate of thickness altogether. 
The Catskill—most massive of all, reaching seven thous 
feet in many places, consisting of sandstone and shale, and 
taining at its last descent beneath the Alleghany Mountains 
thickness of two thousand six hundred feet—may, "I 
danger of exaggeration, be considered the equivalent of 
bed of sandstone one thousand feet thick. 
The Pocono, varying from more than one thousand Pi 
east to two hundred feet in the west, may represent another W 
hundred-foot mass. 
A similar thickness may be given to the Po pi 
boniferous Conglomerate, and we shall then have, a5 the: © 
alent of the great palzozoic sandstones of Pennsylvania, 
three thousand feet of sandstone,—a low estimate. 
The Catskill and Pocono, having no soft beds between 
may, for our present purpose, be counted as one sandstoné q 
In all these sandstones a part of the mass consists of g 
of milky quartz. This feature in the Pottsville, P 
Lower Medina is so strongly developed that they "°°" — 
ttsville, or 3 
