84 CHARACTERS OF STRATA 



regulated by its final state, namely the density conse- 

 quent on its consolidation. 



Thus, in a single series of two strata, the heaviest 

 body might be uppermost ; and, in fact, if quartz and 

 ferruginous clay were suffered to subside together in 

 water under agitation, that would be the case. As, in 

 the present view of stratification, these subsidences 

 have been gradual, and the consequence of distant 

 and distinct operations, the whole objection falls to 

 the ground, 



It is as little an objection to the theory of successive 

 stratification, that crystalline and earthy rocks alter- 

 nate ; since, under the innumerable variety of circum- 

 stances in which they have been formed, or to which 

 they may have been exposed, and tinder the great 

 variety of composition which they present, it would 

 be much more surprising were this not the case. I 

 need dwell on this supposed difficulty no longer ; as 

 the Geologist, who is inclined to examine the various 

 cases that may occur, will find a guide to assist him in 

 the chapter which treats of the consolidation of rocks. 



The mixtures, gradations, and alternations, which 

 take place between strata of different natures where 

 they meet, have given rise to much dispute and spe- 

 culation ; but they do not appear difficult of explana- 

 tion, on the simple principles which are indicated, 

 here, and in various parts of this work. The expla- 

 nations of individual cases must however depend on a 

 variety of minute and local particulars, of which the 

 explanation would be tedious, or, for want of minute 

 and local knowledge of events long past, difficult. 



Where clay and sand, to reassurne a fundamental 

 and easy case, are subsiding from water, it is obvious 

 that there might be a race run, or a contest for time, 



