OF THE EARTH. 459 



interval of time had elapsed between the termination 

 of the inferior and the generation of the superior 

 series. 



This evidence consists in the fragments of previous 

 rocks imbedded in the later strata, or in the nature 

 and composition of the conglomerates. By means 

 of these also, we can sometimes trace, though in an 

 imperfect and general manner only, the sources 

 whence the newer strata were derived ; and thus they 

 also afford some light towards determining the ques- 

 tion of locality or limit, with respect to particular 

 deposits. The mode in which these rocks are cal- 

 culated to afford this evidence ought already to be 

 apparent. The local conglomerates, formerly distin- 

 guished from the general ones, do not enter into this 

 question, as they have originated in local causes of 

 another kind. The trap conglomerates are equally 

 excepted, as depending on revolutions in which this 

 family of rocks is separately engaged. But the ge- 

 neral ones, consisting of the fragments of different 

 rocks, agglutinated by materials of a finer kind, are 

 formed out of the alluvia which, in a former state of 

 the surface, were the produce of these. As the frag- 

 ments of the present strata, produced by the action of 

 the wasting forces, are now forming beds in such 

 places as are fitted to receive them, so are these de- 

 stined to produce future conglomerates, should other 

 revolutions, similar to the past, occur. And as these 

 accumulations necessarily bespeak a long period of 

 time, so do those which enter into the conglomerate 

 rocks equally indicate a long interval, during which 

 the substances out of which they are formed, occu- 

 pied a place above the waters or constituted a dry land 

 marked by hill and valley, and subjected, as the 

 present is, to the action of riverb. The great depth 



