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GEOLOGY OF THE FOURTH DISTRICT. 
CHAPTER VI. 
OLD RED SANDSTONE. 
Catskill group; Montrose and Oneonta sandstone of the Reports. 
(No. 11 of the Pennsylvania Survey.) 
The rocks now recognized as belonging to the Old Red Sandstone, where fully developed, 
consist of various strata of sandstone, shale and shaly sandstone, conglomerates and impure 
limestones. The prevailing color of the arenaceous portion is brick-red, though often lighter, 
and sometimes of a deeper color from a larger proportion of iron ; while the coarser parts are 
often grey, and the shales are green. Beds of green shaly sandstone are interstratified with 
the red friable sandstone, and these are succeeded by a compact kind of conglomerate rock. 
The strata rest conformably upon the grey, olive and greenish shales and sandstones of the 
Chemung group, and pass beneath the conglomerate of the Coal measures. (See Section, 
Plate 7, and woodcut below.) 
In the Fourth District, this formation is of no great thickness or extent; but in passing 
eastward, we find it expanding and augmenting in thickness, till finally it rises in the high and 
prominent peaks of the Catskill mountains, the highest of which has an elevation of more than 
three thousand feet above the level of the sea. From the diminution of the lower groups, the 
base of this formation approaches the base of the mountains, giving a great part of their 
elevation for its thickness. 
Along the Genesee river, and in some of the higher hills south of the Canisteo in Steuben 
county, it consists of a thin mass of calcareous sandstone, highly charged with iron, and con¬ 
taining remains of fishes. By tracing it southward, it is found to expand, and presents many 
of the features of the same farther east. It rises from beneath the Coal measures of Penn¬ 
sylvania, extending northward, and resting upon the rocks of the Chemung group, as in 
England it does upon the Ludlow formation, the equivalent of the latter.* 
1. Chemung group. 2. Old Red sandstone. 3. Conglomerate, and diagonally laminated sandstone. 4. Coal measures of 
Pennsylvania. 
Compare the woodcuts, No. 128, and Plate 7, with the sections, Plates 31, 33, &c. of Silurian Researches. 
