1893.] NEW YORK ACADEMY OF SCIENCES. 103 



with a little mica, and varying quantities of ferric oxide. The 

 latter is sometimes so abundant that that the rock has been 

 mined as an iron ore. 



Where much folded, the sandstone often has the appearance 

 of a breccia, made up of thin, angular fragments. On close 

 examination, these fragments prove to be bits of sandstone, and 

 the brecciated character is seen to be due to a shattering of the 

 rock by pressure, as stated by Emmons*. It is easy to find 

 every stage between the unchanged rock and that which has 

 been reduced to small fragments, recemented by subsequent 

 infiltration. 



Comparing this result of pressure with that i^roduced b}- the 

 same cause in the limestone, a marked contrast is presented. 

 In the sandstone the effect is largely mechanical — a breaking 

 of the rock. In the limestone, chemical changes and crystal- 

 lization are the prominent result. 



Crossbedding on a large scale is very conspicuous in the 

 sandstone, often obscuring the true dip. Concretions also are 

 abundant in some localities, two apparently distinct kinds being- 

 found — small si^herical and large cj^lindrical. The former have 

 been mentioned by Brooksf, the latter by Hough|. The small 

 concretions resemble closely those that are found in many other 

 formations, but the large ones are peculiar. Of cylindrical 

 form, one to twenty feet in diameter, and perhaps six feet, they 

 usually stand perpendicular to the bedding, and their appear- 

 ance is striking. The material of the concretions does not 

 differ from that of the surrounding rock, and the causes are 

 obscure, which explain why it should be arranged as it is, in 

 successive layers, concentric about a line. The age of the 

 sandstone was stated by Emmons to be Potsdam, and such it 

 has been always considered by later writers. Though no fossils 

 have been found in this immediate vicinity, there seems to be 

 no reason for doubting the correctness of this view. 



Relation of Sandstone to Limestone. — There is some confusion 

 in Emmons' discussion of the relation between the sandstone 

 and the limestone. He classes the limestone as primitive and 

 yet plainly implies that it is younger than the sandstone. For 

 he desci'ibes disturbance and contact metamorphism in the 

 sandstone produced by the supposed intrusion of igneous 



* Geology of New York, 2d District, page 104. 



t American Journal of Science, iii., IV., p. 25. 



t Hough, F.B., 3d Ann. Kept. Kegts. Univ. N. Y., p. 32; also Amer. Associa- 

 tion Proc. IV., p. 362. 



