On the Structure and Position of Eozoon Canadense. 285 



present time. We are thus carried back to a period so far 

 remote, that the appearance of the so-called Primordial Fauna 

 may be considered a comparatively modern event." 



Clear evidence had been found in the constitution of the 

 Laurentian and Huronian rocks, that the same chemical and 

 mechanical processes which have ever since been at work in 

 disintegrating and reconstructing the earth's crust, were then 

 in operation ; the great question remaining for determination 

 was, whether vital activity had any place in those ancient seas, 

 or whether they Were altogether untenanted by living beings. 



This question might be presumptively answered in the 

 affirmative by two important sets of facts. In both the 

 Upper and the Lower Laurentian series there are several 

 zones of Limestone, each of sufficient volume to constitute an 

 independent formation. The aggregate thickness of these is 

 said by Dr. Bigsby to be not less than 5000 feet thick. 

 Similar limestones occur in Scotland, and also in Norway and 

 Finland, where they form beds of 1000 feet or more in 

 thickness. Since these limestones are in a highly crystalline 

 condition, the apparent absence of fossils in them could not 

 be considered as in any way negativing the probability that 

 they had been originally formed by the agency of animal life, 

 and subsequently altered by metamorphic action — such being 

 now universally admitted to have been the history of many 

 newer limestones in which there is a like absence of any 

 distinguishable organic remains. So, again, the occurrence 

 of carbon — which, in the form of graphite, both constitutes 

 distinct beds, and is disseminated through the calcareous or 

 siliceous strata of the Laurentian series, as well in Norway as 

 in Canada; — might be taken as an evidence of the existence of 

 vegetation during that epoch, since no one disputes the 

 organic origin of this mineral in more recent rocks. Further, 

 Sir William Logan had observed that certain of the Laurentian 

 marbles, on being struck, gave forth the same overpowering 

 smell of carburetted hydrogen, as is well known to be given 

 off from many beds of carboniferous limestone, whose organic 

 origin is most distinct. And Mr. Sterry Hunt, the accom- 

 plished mineralogist of the Canadian survey, had argued for 

 the existence of organic matters on the earth's surface during 

 the Laurentian period, from the presence of great beds of iron- 

 ore, and from the occurrence of metallic sulphurets. 



But however strong might be these presumptions, con- 

 sidered either separately or collectively, they could not be 

 regarded as in themselves by any means sufficient to 

 establish so important a conclusion, as the dating-back the 

 commencement of organic life from the Lower Cambrian 

 epoch, to the immeasurably more remote period during which 



