1865.] 



LOGAN — LAURENTIAN FOSSILS. 



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lowed by many more. Although the Lower 

 and Upper Laurentian rocks spread over 

 more than 200,000 square miles in Canada, 

 only about 1500 square miles have yet been 

 fully and connectedly examined in any one 

 district, and it is still impossible to say 

 whether the numerous exposures of Lau- 

 rentian limestone met with in other parts 

 of the province are equivalent to any of the 

 three zones, or whether they overlie or un- 

 derlie them all. 



Fig. 2. — Section across Trembling 

 Mountain (21 miles). 



/ f e & d 



b. Upper Laurentian. e'. Second limestone. 



c. Fourth gneiss. e. Second gneiss. 

 df '. Third limestone. f . First limestone. 



d. Third gneiss. f. First gneiss. 



In the examination of these ancient rocks, 

 the question often naturally occurred 

 to me whether, during these remote 

 periods, organic life had yet appeared on 

 the earth. The apparent absence of fossils 

 from the highly crystalline limestones did 

 not seem to offer a proof in negation, any 

 more than their undiscovered presence in 

 newer crystalline limestones, where we have 

 little doubt they have been obliterated by 

 metamorphic action ; while the carbon 

 which, in the form of graphite, constitutes 

 beds, or is disseminated through the calca- 

 reous or siliceous strata of the Laurentian 

 series, seemed to be an evidence of the ex- 

 istence of vegetation, since no one disputes 

 the organic origin of this mineral in more 

 recent rocks. My colleague, Dr. T. Sterry 



