226 ON THE ORIGIN, MATERIALS, COMPOSITION, 



the remains of rocks, of which the greater part has dis- 

 appeared to form the present secondary strata ; nor, 

 in the revolutions of ages, can we decide on what has 

 vanished and what the state of the more antient sur- 

 face was. That it furnished a vegetable creation, and 

 to a great extent, is evinced by the phenomena of 

 coal strata, and by the enormous masses of 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. 



Though it has thus been shown, that with certain 

 rocks more or less completely furnished by animals, 

 the secondary strata consist of the ruins of more antient 

 ones, it is necessary here 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 grada- 

 tion from the coarsest conglomerate, formed of many 

 discordant rocks, to the finer sandstones, that we be- 

 come convinced of the truth of this supposition. 



As also it was attempted to trace in nature the 

 analogy between the finer rocky strata and the pre- 

 sent deposits of sand and clay from water, so, in the 

 superficial or deep-seated alluvia of a coarser nature, 

 we find the prototypes of the present conglomerates ; 

 of the consolidated alluvia, whatever their origin and 

 position may have been, of former worlds. The na- 

 ture of the evidence which these rocks afford with 

 respect to the revolutions of the earth's surface, will 

 be considered in a subsequent chapter, (Chap, xxi;) 



