550 Geological Society : Mr. Lyell on the Recession 



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, 1st, 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 

 the cataract a precipice, beneath which occurs the shale, also 80 feet 

 thick. 



4. The Protean group. — Under the water at the base of the Falls 

 crop out the higher beds of this formation, the name of which has 

 been derived from the variable nature of its component strata. In 

 the district more particularly described in this paper the group is 

 only 30 feet thick, but farther to the eastward it attains thrice those 

 dimensions. On the Niagara it consists of 25 feet of hard limestone, 

 resting on 4 feet of shale ; while at Rochester, eighty miles to the 

 eastward, it comprises, among other beds, a dark shale with grapto- 

 lites, or fossiliferous iron ore, and beneath them a limestone full of 

 Pentamerus oblongus and P. Icevis, considered by Mr. Conrad to be 

 one species. On account of the occurrence of this shell, the whole 

 of these strata have been separated from the Niagara series. 



5. Ontario group.— About half a mile below the Falls the upper- 

 most beds of the Ontario group crop out. At the whirlpool they 

 have a thickness of 70 feet, and at Queenstown of 200, but to the 

 latter dimension must be added 150 feet of inferior beds, exposed 

 between Queenstown and Lake Ontario. The entire group con- 

 sists of 



1 . Red marl with beds of hard sandstone in its "| „„ , , 



upper division 



*} 



