292 GROUPS OF ALLIED SPECIES Chap. IX. 



the Eozoon was found ; and Sir W. Logan states that their 

 " united thickness may jiossibly far surpass that of all the suc- 

 ceeding rocks, fiom llie base of the paleozoic series to the pres- 

 ent time. We arc thus carried back to a period so remote, 

 that the appearance of the so-called Primordial fauna (of 

 Barraudc) may by some be considered as a comparatiyely 

 modern eyent." The Eozoon belongs to the most lowly or- 

 ganized of all classes of animals, but for its class is highly organ- 

 ized ; 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 vast periods which had probably 

 elapsed before the Cambrian system, are almost the same with 

 those since used by Sir W. Logan. Nevertheless, the difliculty 

 of assigning any good reason for the absence beneath the up- 

 per Cambrian formations of vast piles of strata rich in fossils, 

 is very great. It does not seem probable that the most an- 

 cient beds have been quite worn away by denudation, or that 

 their fossils have been wholly obliterated liy raetamorphic ac- 

 tion, for if this had been the case we should have found only 

 small remnants of the formations next succeeding them in age, 

 and these -would always have existed in a partially-metamor- 

 ])hoscd condition. But the descriptions which we possess of 

 the Silurian deposits over immense territories in Russia and in 

 North America, do not support the view, that the older a for- 

 mation is, the more it has invariably suffered extreme denuda- 

 tion and metamorphism. 



The case at present must remain inexplicable ; and may be 

 truly urged as a valid argument against the views here enter- 

 tained. To show that it may hereafter receive some explana- 

 tion, I will give the following hypothesis : From the nature ot 

 the organic remains which do not appear to have inhabited 

 profound depths, in the several formations of Europe and of 

 the United States; and from the amount of sediment, miles in 

 thickness, of Avhich the formations arc composed, we may 

 infer that from first to last large islands or tracts of land, 

 whence the sediment was derived, occurred in the neighbor- 

 hood of the now existing continents of Europe and North 

 America. But we do not know what Avas the state of tilings 

 in the intervals between the several successive fonnations ; 

 whether Europe and the United States during these intervals 

 existed as dry land, or as a submarine surface near land, on 

 which sediment was not deposited, or as the bed of an open 

 a lid unfathomable sea. 



