208 Dr. Mac Culloch on the Origin^ Materials , 



vegetable matter deposited through uncounted ages, and amid a 

 series of partial revolutions of which we can scarcely form an 

 idea. 



Of the Formation of Conglomerate Rocks. 



Tliough it has thus been shewn that, with certain rocks more 

 or less completely furnished by animals, the secondary strata con- 

 sist of the ruins of more ancient rocks, it is necessary, in treating 

 on the origin and nature of these compounds, to bestow a few 

 paragraphs on the conglomerate rocks, since they present some 

 peculiarities of origin that require notice, and since they offer the 

 most perfect evidence of the mechanical nature of the process by 

 which the strata have been principally formed. It is indeed by 

 tracing the gradation from the coarsest conglomerate, formed of 

 many discordant rocks, to the finer sandstones, that we become 

 convinced of the truth of this supposition. 



As also, in nature, we can trace the analogy between the finer 

 rocky strata and the present deposits of sand and clay from water, 

 so in the superficial or deep-seated alluvia of a grosser kind, we 

 find the prototypes of the present conglomerates, of the consoli- 

 dated alluvia of former worlds. The nature of the evidence 

 which these rocks aiford with respect to the revolutions of the 

 earth's surface, belongs to a subject on which I cannot here enter; 

 but it is necessary to distinguish between those which are of a 

 local and those which are of a more general nature. 



These rocks are found, both in the ancient and recent series ; 

 and, in both, under circumstances precisely similar, if differing 

 in extent. They are properly divisible into general and local ; 

 and it is only indeed by thus distinguishing them, that we can 

 derive any advantage, in our reasonings on events, from the evi- 

 dences they afford, or avoid the confusion to which, from incorrect 

 observation, they have frequently given rise. As, in both the se- 

 condary and primary series, similar accidents have occurred, in 

 the fracture, displacement, and transference of strata, it is natural 

 to expect that the conglomerates, here called local, which have 

 resulted from these changes, should be found in both, With re- 



