CuAP. IX. IN LOWEST FOSSILIFEROUS STRATA. ogj 



■\vitli livinp; creatures. Here we encounter a formidable objec- 

 tion ; for it sceins dou])tful whether the eartli in a lit state for 

 the habitation of livin"^ creatures has lasted lono; cnouo-h. Sir 

 W. Tiionipson concludes that the consolidation of the crust can 

 hardly have occurred less than 20 or more than 400 million 

 years ago, Ijut probably not less than 98 or more than 200 mill- 

 ion years. Tliese very wide limits show how doubtful the 

 data are ; and other elements may have to be introduced into 

 tlie problem. Mr. C'roll estimates that about 00 million years 

 have elapsed since the Cambrian period, but this, judging from 

 the small amoiuit of organic change since the commencement 

 of the Glacial epoch, seems a very short time for the many and 

 great mutations of life, which have certainlv occurred since the 

 Cambrian formation; and the previous 140 million years can 

 hardly be considered as sufficient for the development of the 

 varied forms of life which certainly existed toward the close of 

 the Cambrian period. It is, however, probable, as Sir ^\^ 

 Thompson insists, that the world at a verj- early period was 

 subjected to more rapid and violent changes in its physical con- 

 ditions than those now occurring; and such changes would 

 have led to corresponding rapid changes in the organic being-s 

 which inhabited the world at this remote period. 



To the question why we do not hnd rich fossiliferous de- 

 posits belonging to these assumed earliest periods, I can give 

 no satisfactory answer. Several eminent geologists, with Sir 

 li. Murehison at their head, were until recently convinced that 

 we beheld in the organic remains of the lowest Silurian stratum 

 the first dawn of life. Other highly-competent judges, as Ja-qM 

 and E. Forbes, have disputed this conclusion. We should not 

 forget that only a small jiortion of the world is known with ac- 

 curacy. Not long ago, M. Barrande added another and lower 

 stage, abounding with new and peculiar species beneath the 

 old Silurian system. Henmants of several forms have also 

 been detected beneath BaiTande's so-called primordial zone in 

 the Longmynd group, now divided into two stages, and con- 

 stituting the Lower Cambrian system. The presence also of 

 ])hosphatie nodules and bitunnnous matter in some of the low- 

 est azoic rocks, jirobably indicates life at these periods. Now 

 the great discovery of the Eozoon in the Laurent ian f(jrmation 

 of Canada has been made, for, after reading Dr. Carpenter's 

 description of tliis fossil, it is scarcely possible to doubt regard- 

 ing its organic nature. There are tiiree great series of strata 

 beneath tiie Siluriiin svslein in Canad:i, in the lowest of which 



