Geology and Topography of Western New York. 87 



evidently been exposed. The deep valleys, which penetrate this 

 formation in a southerly direction from the great limestone terrace; 

 the dividing ridges, also, which have their northern terminations 

 on the same terrace, becoming more rugged and mountainous as 

 they approach the Pennsylvania state line, with their sides deeply 

 furrowed by precipitous gullies and ravines, are sufficient proofs 

 that other causes of denudation than the insignificant streams 

 which traverse these valleys, have been in operation. 



'One peculiar feature, which adds greatly to the picturesque 

 scenery of Western New York, arises from the fact that many of 

 these valleys have been excavated to a level below the general 

 escarpment of the limestone terrace,* which consequently forms 

 a barrier at their mouths, and gives rise to most of those beautiful 

 sheets of water so justly admired by the lovers of fine scenery. 

 This feature will again be alluded to further on. 



The aggregate thickness of the rock strata, from Lake Ontario 

 to the northern outcrop of the coal in Pennsylvania, is estimated 

 by Mr. James Hall at six thousand and fifty one feet.f How far 

 they extended to the north, and whether the primitive regions on 

 either or both sides of the St. Lawrence, were originally overlaid 

 by them, are questions difficult to solve, and which require the 

 minute and careful examination of the geologist. There are 

 some circumstances, however, which seem, to favor this conclu- 

 sion. It is stated by Dr. Bigsby,;]: when speaking of the hori- 

 zontal limestone of the Canadas, that " this limestone forms a 

 horizontal girdle around the trap mountain of Montreal, from 

 which, as from a centre, large veins or dykes radiate into the ad- 

 joining limestone to the distance of two miles in some cases to 

 my own knowledge, and even to La Chine, according to informa- 

 tion received from M. Burnett, chief engineer to the La Chine 

 Canal. The limestone in its upper strata, is brown and crystal- 

 line, but black, compact, and slaty below. It contains in immense 

 quantities the organic remains peculiar to the mountain limestone 

 of England and Ireland." It is also stated by Prof. Vanuxem,*§) 



* Since writing the above, my attention lias been called to the fact that Mr. 

 David Thomas communicated this phenomenon to Prof. Eaton in 1830. See Amer- 

 ican Journal, Vol. xviii. p. 376. 



t New York Geological Report, 1838. See Atlas. 



X American Journal, Vol. VIII. p. 71. 



§ New York Geological Report, 1838, p. 255. 



