Quebec Group of Logan. 135 



as these exist further to the west; hut to this should be 

 added his expositions in the Geology of Canada, 1863, and 

 in his note appended to Murray's Report on Newfoundland 

 in 1865, in which he explains the peculiar character of the 

 series as a sub-marginal or marginal group, distinct in 

 structure because of its special conditions of deposit from 

 the equivalent formations of the interior plateau. This 

 distinction has been subsequently elaborated and enforced 

 by the writer, 1 and lies at the foundation of any scientific 

 conception of the general geology of Eastern America and 

 Western Europe. Hence one important element in the 

 value of the name as well as of the thing designated. 



As Logan's summary of this subject in the Newfoundland 

 Report is comparatively little known, it may be useful to 

 quote a few sentences of it here, bearing in mind that it 

 was written twenty -five years ago, whon many of our pre- 

 sent geologists were in their school-boy days. 



" The sediments, which in the first part of the Silurian 

 period were deposited in the ocean surrounding the Laur- 

 entian and Huronian nucleus of the present American 

 continent, appear to have differed 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 Potsdam to the 

 Hudson River formation. But between the Potsdam and 

 Chazy periods, a sudden continental elevation, and subse- 

 quent gradual subsidenee, allowed the accumulation of a 

 great series of intermediate deposits, which are displayed 

 in the Green Mountains, 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 disloea- 



1 The Quebec Group, Canad. Naturalist, 1879. Address to 

 British Association, 1886. Palaeozoic Rocks of Eastern America, 

 Journ. Geol. Soc, 1888. 



