No. 3.] NATURAL HISTORY SOCIETY. 171 



treoloaists of the United States, that the iireat reversed fault was 

 a true stratigraphical superposition, and consequently that these 

 strange deposits were newer tlian those to the west of them. 

 But so soon as the actual nature of the case was made manifest, 

 and this was first due to a right apprehension of the fossils, for 

 which Mr. Billiu£rs deserves much of the credit, Sir William at 

 once and for ever apprehended the real conditions of the problem, 

 and set himself to work it out on the true line of investioation. 



In evidence ol' this, and as presenting as clear a view of the 

 wliole matter as any we can give, up to the present time, I quote 

 from a note by Sir William appended to Mr. Murray's report on 

 Newfoundland for 18G5. and which is less known than his utter- 

 ances on this subject published in the Canadian reports: 



'• The sediments which in the first part of the Silurian period 

 were deposited in the ocean surrounding the Laurentian and 

 Huronian nucleus of the present American continent, appear to 

 have diff"ered considerably in different areas. Oscillations in this 

 ancient land permitted to be spread over its surface, when at 

 times submerged, that series of apparently conformable deposits 

 which constitute the New York system, ranging from the Pots- 

 dam to the Hudson River formation. But between the Potsdam 

 and Chazy periods, a sudden continental elevation, and subsequent 

 jiTadual subsidence, allowed the accumulation of a 2:reat series of 

 intermediate deposits, which are displayed in the Green Moun- 

 tains, on one side of the ancient nucleus, and in the metalliferous 

 rocks of Lake Superior, on the other, but which are necessarily 

 absent in the intermediate region of New York and central 

 Canada. 



'' At an early date in the Silurian period, a great dislocation 

 commenced aloni>- the south-eastern line of the ancient irneissic 

 continent, which i>ave rise to the division that now forms the 

 western and eastern basins. The western basin includes those 

 strata which extended over the surface of the submerged conti- 

 nent, together with the Pre-chazy rocks of Lake Superior, while 

 the Lower Silurian rocks of the eastern basin present only the 

 Pre-chazy formations, unconformably overlaid, in parts, by Upper 

 Silurian and Devonian rocks. The group between the Potsdam 

 and Chazy, io the eastern basin, has been separated into three 

 divisions, but these subdivisions have not yet been defined in the 

 western basin. In the western basin the measures are compara- 

 tively flat and undisturbed ; while in the eastern they are thrown 



