Geology and Topography of Western New York. 95 



Hudson ; forming for itself a channel through the Highlands, if 

 that pass did not previously exist. 



The large quantity of primitive boulders scattered over the sur- 

 face, and distributed promiscuously through the diluvium, would 

 seem to indicate some such movement. That they came from 

 the north, has often been suggested; and the fact, that the near- 

 est primitive rocks, in place, occur in that direction, renders the 

 assumption highly probable. I have noticed one within the 

 boundaries of this city, containing the Labradorite. It is doubt- 

 less identical with the Hypersthene rock in Essex county,* or 

 with a similar rock described by Dr. Bigsby, as occurring on the 

 northeast coast of Lake Huron,f and probably came from one of 

 those locations. That loose masses of rock have been frozen into 

 cakes of ice, and widely distributed over the surface of the earth, 

 seems to admit of no doubt, as the same phenomenon may be 

 witnessed in all currents of the ocean which flow from high lati- 

 tudes towards the equator. 



But by whatever agent these boulders have been transported, 

 whether by the buoyancy of congealed water, and dropped in a 

 more southern latitude, when disencumbered of their icy bark, or, 

 swept along by the unaided force of currents, tides and waves, 

 they have left their " marks" engraven on the surface of the 

 limestone rocks, in characters Avhich bid fair to prove indelible, 

 and by which we may obtain a clew to their early history. 



The Niagara river takes a course at right angles to the general 

 direction of Lake Erie, and, in its descent to Lake Ontario, cuts 

 directly across the limestone terrace, which, at this point, exceeds 

 thirty miles in breadth. The upper strata of this lime-rock, con- 

 tain layers and strings of chert, which form a kind of net-work, 

 and render them almost incapable of disintegration from ordinary 

 causes. These strata form both the barrier at the outlet of Lake 

 Erie, and the rapids, between Buffalo and Black Rock. Below 

 the northern outcrop of these cherty layers, which may be re- 

 garded as forming a kind of step on the terrace, and upon those 

 strata which terminate at the mountain ridge, lie the shallow val- 

 leys of the Tonnewanda and Chippewa creeks, one of which 

 flows to the west, and the other to the east; both entering the 

 Niagara between Black Rock and the Falls. 



* See New York Geological Reports, 1837 and 1838. 

 t American Journal of Science, Vol. thi. p. 69. 



