of the Falls of Niagara. 549 



structure of the country. Mr. R. Bakewell in 1830*, published an 

 account of the country adjacent to the Falls, and Mr. De la Beche 

 in 1831 f» endeavoured to point out the gradual manner in which 

 the receding Falls, if they should ever reach Lake Erie, would dis- 

 charge the waters of the lake; Prof. D. Rogers also in 1835 J 

 showed distinctly, that, as the Falls retrograde, they would cut 

 through rocks entirely distinct from those over which the waters are 

 now precipitated, and correctly represents the superior limestone at 

 Buffalo as newer than the limestone of the Falls, though he omits 

 the intervening saliferous formation. Mr. Conrad likewise, in his 

 Report for 1837 §, first assigned all the formations of the country to 

 the Silurian system ; but to Mr. James Hall (1838) || is due the merit 

 of having shown the true geological succession of rocks of the di- 

 strict. 



The contents of the memoir may be divided into two parts : I. an 

 account of the successive strata of the Niagara district ; and II. a 

 description of the phenomena exhibited by the Falls. 



I. His sketch of the geology of the district, the author states, is 

 derived either from the published surveys of Mr. Hall, or from the 

 information he obtained while travelling with that gentleman in the 

 State of New York during the autumn of 1841 ; and he acknow- 

 ledges the great advantage he derived from the facilities thus afforded 

 him. The strata between Lakes Erie and Ontario appear to belong 

 to the middle and lower portions of the English Silurian system, and 

 they are divisible into the following five principal formations: 1st. 

 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 Silunan 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 



* Loudon's Magazine of Natural History, 1830. 



f Manual ofGeology, three editions, 1831, p. 55; 1832, p. 55; 1833, p. 60. 



X Silliman's Journal, vol. xxvii. p. 326. 



§ States' Report of the Geology of NewYork. 



|| Geological Report of the State of New York for 1838. 



