ASSUMED UNlVEKSALrrY OF 8TKATIFIED GEOUPS. 323 



" Bill," it will perhaps be said, " though iiidividual 

 strata are not continuous over large areas, yet systems of 

 strata are. Thouo-h within a few miles the same bed jjrad- 

 ually passes from clay into sand, or thins out and disap- 

 pears, yet the group of strata to which it belongs does not 

 do so ; but maintains in remote regions the same relations 

 to other groups." 



This is the generally-current belief. On this assump- 

 tion the received geological classifications appear to be 

 framed. The Silurian system, the Devonian system, the 

 Carboniferous system, etc., are set down in our books as 

 groups of formations which everywhere succeed each other 

 in a given order; and are severally everywhere of the same 

 age. Though it may not be asserted that these successive 

 systems are universal ; yet it seems to be tacitly assumed 

 that they are so. In North and South America, in Asia, 

 in Australia, sets of strata are assimilated to one or other 

 of these groups ; and their possession of certain mineral 

 characters and a certain order of superposition are among 

 the reasons assigned for so assimilating them. Though, 

 probably, no competent geologist would contend that the 

 European classification of strata is applicable to the globe 

 as a whole ; yet most, if not all geologists, write as though 

 it were so. Among readers of works on Geology, nine out 

 ten carry away the impression that the divisions. Primary, 

 Secondary and Tertiaiy, are of absolute and uniform appli- 

 cation ; that these great divisions are separable into subdi- 

 visions, each of which is definitely distinguishable from the 

 rest, and is everywhere recognizable by its characters as 

 Buch or such ; and that in all parts of the Earth, these 

 minor systems severally began and ended at the same time. 

 When they meet with the term " carboniferous era," they 

 take for granted that it was an era universally carbonife- 

 rous—that it was, what Hugh Miller indeed actually de- 

 gcribes it, an era when the Earth bore a vegetation far 



