No. 136.] 25 



like those of the present, or whether a variety of plans and 

 different forms of animated existence had maintained a long 

 series of changes, of which the present inhabitants of earth are 

 only the latest arrangement. 



Now this is precisely what we have in the stratified rocks, and 

 this study of the order of organic creation, as displayed in their 

 buried contents, is the chief object of Geology ; the reading of 

 the history of earth from its own natural records, formed in the 

 way we have noticed. 



That these stratified rocks are really old sea-deposits, is per- 

 fectly proved by their form corresponding to that produced by 

 deposition from water, by their buried relics of shells and fishes 

 and other remains, by the ripple-marks so plainly visible on the 

 surfaces of many layers, and other evidences. Their present 

 hardness is chiefly the effect of chemical action among their par- 

 ticles, or of consolidation by their own weight and the pressure 

 of higher layers. Their present elevated position is due either 

 to their having been uplifted by subterranean forces above their 

 parent sea, or to the recession of its waters to deeper basins 

 formed by the subsidence of other parts of the earth's surface, 

 both causes having doubtless combined to produce the result. 



The broken and abrupt form in which we often find these strata 

 now to exist, projecting their edges from the banks of ravines or 

 slopes of high hills, is explained by the consideration that during 

 their slow emergence from the sea, they were subjected to the 

 wearing action of waves and marine currents which must have 

 removed considerable portions of them ; and that ever since then 

 the action of rains and streams during enormous periods have 

 carried on the wearing (or, as geologists call it, the "denuding") 

 process to the point at which it now stands ; the whole series of 

 strata, many thousand feet in thickness, being deeply worn and fur- 

 rowed into hills and valleys. These processes are difficult to trace, 

 for their effect has been always to obscure in one period what. was 

 done in a previous one ; but the evidences of enormous wear are 

 visible to every observer who studies the face of the country. 



These stratified rocks (as might be presumed from this view of 

 their origin) lie, not as many unobservant persons think, in shape- 

 less masses, left confusedly here and there, but in vast sheets or 

 widely extended layers. Many of these, though only a few feet 

 in thickness, extend from one extremity of the State to the other, 

 [Assembly, No. 136.] 4 



