360 ORIGIN OF SPECIES 



cient for the development of the varied forms of life which 

 already existed during the Cambrian period. It is, however, 

 probable, 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 

 corresponding rate in the organisms which then existed. 



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

 posits belonging to these assumed earliest periods prior to the 

 Cambrian system, I can give no satisfactory answer. Sev- 

 eral 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 that 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 in South 

 Wales beds rich in trilobites, and containing various molluscs 

 and annelids. The presence of phosphatic nodules and bitu- 

 minous matter, even in some of the lowest azoic rocks, prob- 

 ably indicates life at these periods ; and the existence of the 

 Eozoon in the Laurentian formation of Canada is generally 

 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 appear- 

 "ance 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 organised of all 

 classes of animals, but is highly organised for its class; it 

 existed in countless numbers, and, as Dr. Dawson has re- 

 marked, 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 



