682 NOTES TO BOOK XVIII. 



shores of the great continent on which the mammoths 

 lived, the period when the gold ore was formed, and when 

 the watershed of the Ural chain was elevated. 



(CA.) p. 592. Mr. Lyell, in the sixth edition of his 

 Principles, B. i. c. xii, has combated the hypothesis of M. 

 Elie de Beaumont, stated in the text. He has argued 

 both against the catastrophic character of the elevation of 

 mountain chains, and the parallelism of the contempora- 

 neous ridges. It is evident that the former doctrine may 

 be true, though the latter be shown to be false. 



(DA.) p. 593. In proceeding downwards through the 

 series of formations into which geologists have distributed 

 the rocks of the earth, one class of organic forms after 

 another is found to disappear. In the tertiary period we 

 find all the classes of the present world : Mammals, Birds, 

 Reptiles, Fishes, Crustaceans, Mollusks, Zoophytes. In 

 the secondary period, from the Chalk down to the New 

 Red Sandstone, Mammals are not found, with the minute 

 exception of the marsupial amphitherium and phascolothe- 

 rium in the Stonesfield slate. In the Carboniferous and 

 Devonian period we have no large Reptiles, with, again, 

 a minute amount of exception. In the lower part of the 

 Silurian rocks, Fishes vanish, and we have no animal 

 forms but Mollusks, Crustaceans and Zoophytes. 



The Carboniferous, Devonian and Silurian formations, 

 thus containing the oldest forms of life, have been termed 

 palaeozoic. The boundaries of the first life-bearing series 

 have not yet been determined; but the series has in 

 which vertebrated animals do not appear been provi- 

 sionally termed protozoic, and the lower Silurian rocks may 

 probably be looked upon as its upper members. Below 

 this, geologists place a hypozoic or azoic series of rocks. 



