464 THE CANADIAN NATURALIST. [Vol. VI. 



" I think you are acting wisely in studying with time and all ne- 

 cessary care, all the elements of the question before asserting in a 

 positive manner, the order of the succession of these three fauna. As 

 there are many savants interested in the debate which will infalla- 

 bly arise, when you publish your discoveries, it is very desirable that 

 your opinion may be so well founded that it may be inattackable. 



" At all events, it is certain that the labours of the Geological 

 Survey of Canada, will throw a great light on the Geology of the 

 North of America, and in particular on the Silurian Epoch. Naturally, 

 that light will reflect on the ancient continent, and we will be per- 

 mitted to fix our ideas on bases more broad and solid, &c., &c. 



J. Barrande." 



This letter proves that the age of the Point Levis fossils was 

 determined by me before I had written to Barrande about them. 

 It now became almost certain, that the trilobites in the Georgia 

 slates did not constitute a colony. This was confirmed by strati- 

 graphical evidence, in 1861, by J. Richardson, who while making 

 some examinations for our Survey at the straits of Belle Isle, 

 found the fossils of the Georgia slates, in the undisturbed rocks 

 lying directly on the Laurentian. He also discovered them in 

 the same position, in Newfoundland, but in this instance with 

 other rocks holding the fossils of the Potsdam and calciferous 

 above them. The above appears to me to be quite suflScient to 

 show, that the error relating to the Taconic rocks, was removed 

 by the investigations and discoveries of the Geological Survey of 

 Canada. 



In December 1860, Mr. Marcou, who took a very active in- 

 terest in the investigation, published Barrande's opinion on the 

 age of the Georgia slates. This I have always considered to be 

 equivalent to the publication of Barrande himself, as no doubt it 

 was authorized by him. According to the laws of priority, there- 

 fore, Barrande was the first to determine the horizon of this for- 

 mation on paljeontological grounds, and I have on several occasions 

 given him full credit for it. But by so doing, I am not precluded 

 from showing what my own views were. I had previously recog- 

 nized that the fossils were primordial forms, and that eii^her they 

 constituted a colony, or the rocks were older than the Hudson- 

 River group. 



American geology is indebted to Barrande for much greater 

 services. It was he that discovered that, as a general rule, rocks 

 holding trilobites of those types which we now call primordial, 

 lie below the Lower Silurian. It was by the application of 



