120 Mr. Weaver on the Older Stratified 



diura in which they are enveloped, as being of an argillaceous, 

 calcareous, or siliceous natui-e, we can hardly expect to find 

 that the local arrangements of one country should strictly 

 correspond with those of another*. I am persuaded that many 

 general resemblances exist, but that a diversity prevails 

 in the details of different tracts, both with respect to the com- 

 position and disposition of the mineral masses and the distri- 

 bution of the remains of organized bodies. In this view we 

 appear to be borne out by all that is hitherto known of the 

 transition relations of Ireland, England, Scotland, Scandi- 

 navia, Russia, Poland, Germany, Belgium, France, or North 

 America. However, let future and more extended inquiries 

 decide this question. In the mean time it may be remarked 

 that, while in these different countries many of the organic 

 remains correspond as to species, yet peculiar species also 

 occur in some of those tracts which have not yet been found 

 in others. The comprehensive general views expressed under 

 this head by Professor Sedgwick appear to me so truly just 

 and appropriate, that the following extracts from his con- 

 cluding words may be very appositely introduced in this 

 place. 



" Some of the generalizations are, however, founded on 

 imperfect evidence, and to render them more complete, it is 

 now necessary to appeal to the organic remains in the se- 

 veral groups. In this department litde has been yet efifected, 

 excepting in the higher part of the Silurian system, where 

 the upper divisions (at least in one part of the island) assume 

 definite mineralogical and zoological types. "Whether defi- 

 nite geological groups can be made out in any lower system 

 still remains to be seen. The difficulty of classification by 

 organic remains increases as we descend, and is at length in- 

 surmountable ; for in the lowest stratified groups, independ- 

 ently of metamorphic structure, all traces of fossils gradually 

 vanish; and the great range of certain species through nu- 

 merous successive groups, and the very irregular distribution 

 of fossils even in some of the more fossiliferous divisions, add 

 greatly to the difficulties of establishing true definite groups 

 even within the limits of our own island. The difficulties are 

 indefinitely increased in comparing the formations of remote 

 continents. But these circumstances are compensated by the 

 magnificent scale of development of the successive groups, 

 and their wide geographical distribution. Taken together 



« 1 perceive that on this subject there is nearly a coincidence between 

 Mr. Dc la Beche's views and my own, formed independently of each 

 other. See Report on Cornwall, &c. p. 39. 



