lf)4 



ASSUMED DISCOKDANCE OF 



[Ch. V. 



as were their fossil 



analogues 



in the inland strata; and 

 while some of the recent shells of the Adriatic were becoming 

 incrusted with calcareous rock, he observed that others had 

 been newly buried in sand and clay, precisely as fossil shells 



This discovery of the iden- 

 modern and ancient submarine operations was not 



ennme 



m 



enomena 



otherwise 



within the sphere of human observation. 



In like manner, the volcanic rocks of the Yicentin had 

 been studied in the beginning of the last century ; but no 

 geologist suspected, before the time of Arduino, that these 

 were composed of ancient submarine lavas. During many- 

 years of controversy, the popular opinion inclined to a belief 

 that basalt and rocks of the 



same 



from 



sive periods over the continents, charged with the com- 

 ponent elements of the rocks in question. Few will now 

 dispute that it would have been difficult to invent a theory 

 more distant from the truth ; vet we must cease to wonder 



many 



remember 



from 



stance of its confirming the assumed want of analogy between 

 geological causes and those now in action. By what train of 

 investigations were geologists induced at length to reject 

 these views, and to assent to the igneous origin of the trap- 

 pean formations ? By an examination of volcanos now active, 

 and by comparing their structure and the composition of 

 their lavas with the ancient trap rocks. 



The establishment, from time to time, of numerous points 

 of identification, drew at length from geologists a reluctant 

 admission, that there was more correspondence between the 

 condition of the globe at 

 uniformity in the laws whi 



remote 



its surface, than they at first imagined. If, in this state of 

 the science, they still despaired of reconciling every class of 



lenomena 



■> 



limits 



mi 











