318 GROUPS OF ALLIED SPECIES. 



as Sir William Thompson insists, that the world at a very 

 early period was subjected to more rapid and violent changes 

 in its physical conditions than those now occurring ; and such 

 changes would have tended to induce changes at a correspond- 

 ing rate in the organisms which then existed. 



To the question why we do not find rich fossiliferous 

 deposits belonging to these assumed earliest periods prior 

 to the Cambrian system, I can give no satisfactory answer. 

 Several eminent geologists, with Sir R. Murchison 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 Lyell and E. 

 Forbes, have disputed this conclusion. We should not forget 

 than only a small portion of the world is known with accuracy. 

 Not very long ago M. Barrande added another and lower 

 stage, abounding with new and peculiar species, beneath the 

 then known Silurian system ; and now, still lower down in 

 the Lower Cambrian formation, Mr. Hicks has found South 

 Wales beds rich in trilobites, and containing various mollusks 

 and annelids. The presence of phosphatic nodules and bitu- 

 minous matter, even in some of the lowest azotic rocks, 

 probably indicates life at these periods ; and the existence 

 of the Eozoon in the Laurentian formation of Canada is gen- 

 erally admitted. There are three great series of strata 

 beneath the Silurian system in Canada, in the lowest of 

 which the Eozoon is found. Sir W. Logan states that their 

 " united thickness may possibly far surpass that of all the 

 succeeding rocks, from the base of the palaeozoic series to 

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

 remote, that the appearance of the so-called primordial fauna 

 (of Barrande) may by some be considered as a comparatively 

 modern event." The Eozoon belongs to the most lowly 

 organized of all classes of animals, but is highly organized 

 for its class ; it existed in countless numbers, and, as Dr. 

 Dawson has remarked, certainly preyed on other minute 

 organic beings, which must have lived in great numbers. 

 Thus the words, which I wrote in 1859, about the existence 

 of living beings long before the Cambrian period, and which 

 are almost the same with those since used by Sir W. Logan, 

 have proved true. Nevertheless, the difficulty of assigning 

 any good reason for the absence of vast piles of strata rich 

 in fossils beneath the Cambrian system is very great. It 

 does not seem probable that the most ancient beds have been 

 quite worn away by denudation, or that their fossils have 



