360 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



so powerful and well-marked in those localities, and even further east 

 in Wayne County, it thins off rapidly east, and appears there quite 

 subordinate to the Clinton, and almost destitute of its proper fossils. 

 In Oneida County this group is in some places a mere thin sheet of 

 shale with some beds of concretionary limestone, and so is scarcely 

 separable from the Clinton beneath. 



In the parallel of Little Falls the Niagara group goes no further east. 



As before hinted, impoverished and slender as the Niagara has 

 thus become even in the central part of New York, its place is still 

 marked by a thin band of limestone, even as far east as the base of 

 the Helderberg Mountains at Schoharie, and upon the Hudson River 

 at Roudout. This is the Coralline Limestone of Schoharie (4 feet 

 thick), to be spoken of afterwards. Near Schoharie (Hall, Pal. ii. 3) 

 even this thins out as well as the Clinton and Onandago-salt groups, 

 leaving the Hudson-River and Waterlime groups to come into actual 

 contact (De Verneuil, Bullet. Soc. Geol. France, 2 ser. torn. iv. p. 

 655). 



From the centre of the State, westward, the Niagara group, on 

 the contrary, increases in magnitude. At Lockport and on the river 

 Niagara it is 200 to 250 feet thick. 



Near the west end of Lake Erie (Hall, Sill. J. xlii. 53), Niagara 

 limestone appears above the surface of the water, from a subter- 

 ranean uplift. It then, in a S.S.W. direction, forms part of the 

 Cincinnati dome or axis along the borders of Ohio and Indiana. 



In the central and western parts of Ohio the Niagara Limestone 

 forms a most important rock, and is called the " Cliff Limestone " 

 by Professor Locke. " We have, therefore, in these regions," says 

 James Hall, " this condition of things : the Niagara limestone, which 

 commences small in the east part of New York, has acquired great 

 thickness, and has become the most prominent limestone, the Lower 

 Helderberg and Onondaga-salt groups having all but thinned out," 



Throughout this great extent of country (including North Illinois, 

 Wisconsin, and Iowa), and for many miles west of the Mississipi, the 

 upper beds of the true Niagara Limestone are characterized by, 

 among other things, Halysites catenulatus, and often by a Retepora, 

 — the former distinctive of Upper Niagara in Western New York. 



The Niagara group is scarcely seen in Pennsylvania. 



Position. — In New York this is horizontal to common observation ; 

 but there is a slight inclination to the south-west, with gentle undu- 

 lations. 



From Scanandea to Verona (New York) the Niagara group is 

 lifted up and fractured (Vanux. p. 92). At Cincinnati on the 

 Ohio, and for some hundred miles S.S.W. and N.N.E., this group, 

 in like manner with others, suffers a prolonged, low, broad uplift, 

 both with and without rupture. 



Thickness. — It is four feet thick on the Hudson River, and even in 

 the centre of the State the limestone portion is only a few feet more 

 in thickness ; but it enlarges westward to 250 feet at Niagara, and 

 to 1000 feet about the River Mississipi, in the Illinois, &c. (Hall, 

 Sill. Journ. xlv. 158). 



