No. 3.] NATURAL HISTORY SOCIETY. 179 



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should not be needlessly changed, and that they should not be 

 misapplied. 



The name " Quebec Group/' introduced by Sir William Logan, 

 should be retained lor that peculiar development of the rocks of 

 the second fauna, eminently exposed and accessible in the vici- 

 nity of Quebec, to whatever extent its extensions east and west 

 may be circumscribed ; and whatever value may be attached to 

 the local subdivisions into Levis, Lauzon and Sillery. On the 

 one hand, the use of one of these terms, Levis, for the whole, leads 

 to misconception ; and the absurdity of the term " Canadian " 

 (applied in one widely-known text book to the rocks of this age) 

 becomes apparent when we see it made correlative with a purely 

 local name like " Trenton," and when we consider that Canada 

 is a region greater than the United States of America, and with 

 equally varied geological structure. 



The more recent developments in the geology of North xlmer- 

 ica require, as Dr. Hunt and Mr. Selwyn have urged, that the 

 Cambrian system should be recognized as a group altogether 

 distinct from the Silurian ; and whatever views as to the use of 

 these names may ultimately prevail in England, for us the 

 dividing line between the Cambrian and the Siluro-Cambrian or 

 Lower Silurian, unquestionably comes about the horizon of the 

 Potsdam. As to the formations older than the Cambrian, I am 

 disposed to regard the Montalban and Taconian of Dr. Hunt as 

 representing definite groups of rocks, which may however even- 

 tually prove to belong to the base of the Cambrian, with which 

 equivalent strata in the Maritime Provinces of Canada seem to 

 be associated. The Huronian series of Logan represents another 

 great fact in the geology of North America, namely a period of 

 immense igneous ejection and disturbance intervening between 

 the Laurentian and the Cambrian. In the typical Huronian 

 area of Lake Huron it unquestionably rests unconformably on 

 the Laurentian, and is itself overlaid by rocks of Cambrian or 

 still greater age. It has precisely the same mineral characters 

 and position as far east as New Brunswick and Newfoundland, 

 and as far west as the Pacific slope, ^ and is thus one of the most 



* Clartnce King's Report ot the 40th Parallel. The nigged features 

 and precipitous sides of the Laurentian and Huronian exposures in 

 thia region correspond with Logan's view of the steep slope of the 

 Laurentian land at the time of the deposition of the Quebec Group 

 rocks. 



