556 



THE AZOIC SYSTEM AND ITS SUBDIVISIONS. 



portion of the Azoic of Foster and Whitney as developed north of Lake 

 Huron. The two series possess nothing in common beyond the fact 

 that both are basic and both carry copper — one in the native state and 

 the other in the form of the sulphide. Instead of admitting that the 

 acidic and basic rocks of the Azoic formed one mixed series of eruptive 

 and detrital rocks, Logan here left the gneissic and granitic rocks in the 

 Laurcntian and placed the basic ones in a new series — the Iluronian 

 on account of the known unconformability of the Keweenaw Point rocks 

 with the Azoic. Later Logan admitted siih silentio the mistake he had 

 made in uniting the Keweenaw Point rocks with those north of Lake 

 Huron, thereby abandoning the data on which the Azoic was separated 

 into two scries; yet he persisted in his two divisions, which from that 

 time forward in reality rested exclusively on a lithological basis. 



The publication, in 18G3, of a volume ostensibly giving the evidence 

 and data as obtained during the previous years of the survey, but which 

 in reality presented as proved that which had only a theoretical basis, 

 with the evidence largely omitted or disguised, contributed greatly to 

 the overlooking of the previous reports, and the acceptance of this as a 



r 



correct statement of results obtained, and of the nature of the evidence 

 by which they were supported. This was farther aided by the persist- 

 ent misrepresentations of the facts made by Plunt, as pointed out in tiie 

 preceding pages. These misrepresentations have been so persistent and 

 glaring that we are compelled to say that we consider that Hunt's 

 "Chemical and Geological Essays," his "Azoic Rocks," and his publica- 

 tions generally, cannot be taken as any authority as to what ho or any 

 one else has previously taught or held, until his quotations and state- 

 ments shall have been carefully compared with the original publications 

 In this matter we are fully in accord with that which Dana has again 

 and again earnestly claimed. 



If we examine the often repeated statement that the Huronian un- 

 conformably reposes on the worn edges of the Laurentian and contains 

 the debris of the latter, it will be found that in e:\GY-y case in which the 

 rocks referred to these two formation^ were found in contact in the 

 Canadian district (seven in number), the Iluronian, with but two excep- 

 tions, is said to be conformable with and to generally pass imperceptibly 

 into the Laiirentian. In one of these two exceptions the rocks show 

 mutually intrusive relations, and in the other the Iluronian abuts 

 against and runs under the Laurcntian, 



In all cases in which pebbles and fragments of the Laurentian have 



' , J 



been found in the Iluronian, they were seen occurring high up in the 



