596 
they are divisible into the following five principal formations: Ist. 
the Helderberg limestone; 2nd, the Onondago salt group; 3rd, the 
Niagara group; 4th, the Protean group ; and 5th, the Ontario group, 
1. The Helderberg limestone, which has derived its designation 
from the range of mountains of the same name, and is the newest 
formation of the country, is exposed where the Niagara flows out of 
Lake Erie, and on account of the organic remains with which it 
abounds, it is considered to be the equivalent of the Wenlock rocks 
of Mr. Murchison’s Silurian system. The correctness of this stra- 
tigraphical position Mr. Lyell has verified by an examination of the 
succession of formations from the coal-field on the borders of Penn- 
sylvania to the group in question, the intervening deposits consist- 
ing, first, of old red sandstone, having at its bottom a large develop- 
ment of shales and sandstones called the Chemung and Ithaca for- 
mations, but containing organic remains which resemble those of the 
Devonian system; and then 1000 feet of Ludlowville shales with 
fossils analogous to those of the Ludlow rocks of Mr. Murchison. 
The superposition of this vast horizontal series is beautifully ex- 
posed in the banks of the Genessee and other rivers ; and near Le Roy 
as well as elsewhere, the Helderberg limestones crop out from be- 
neath them. On account of the middle portion containing nodules 
and layers of chert, the whole deposit was first called the corni- 
tiferous formation by Prof. Eaton. In this part of the State of New 
York, and still further to the west, in Upper Canada, the limestone 
is only 50 feet thick, whereas at Schoharie in the Helderberg moun. 
tains, 300 miles to the eastward, its thickness is 300 feet. 
2. The Onondago salt group.—This series of beds, Mr. Lyell says, 
is extremely unlike any described member of the European Silurian 
group. With the exception of a stratum of limestone at the top 
containing Cytherina, it consists of red and green marls with beds of 
gypsum, the former being undistinguishable from the marls of the new 
red system of England; and they are also destitute of fossils. Salt 
springs are of frequent occurrence, but no rock salt has been disco- 
vered in the group. ‘The breadth of the zone of country occupied by 
the deposit is not less than 16 miles, and Mr. Hall infers from it and 
the slight southerly dip of the strata, that the entire thickness in the 
neighbourhood of the Niagara is at least 800 feet, an estimate con- 
firmed by the nearest sections eastward of the river. In some parts 
of the State of New York the thickness is not less than 1000 feet. 
Along the Niagara the formation has been greatly denuded, and is 
covered by superficial drift, except at a few places. 
3. The Niagara group.—This series of beds commences near the 
rapids, above the great cataract. It comprises, Ist, the Niagara, or 
Lockport limestone, and 2ndly, the Niagara, or Rochester shale; 
and it contains in both divisions fossils identical with those of the 
Wenlock limestone of England, with others peculiar to North Ame; 
rica. The limestone at the rapids and the Falls is 120 feet thick; the 
upper 40 feet, being thin-bedded, have given way to the frost and the 
action of the stream, but the lower 80 feet, being massive, forms at 
