AND STRATIFICATION. 75 



shall more easily comprehend the truth of this re- 

 mark, and the probable cause in which these dif- 

 ferences have originated. 



The smallest deposits which we know, are those 

 formed in lakes and actuaries ; and if we examine 

 these, although we shall find that they all contain 

 alternations or successions of mud, shells, clay, and 

 sand, yet we shall see that there are probably no two 

 in which these materials are deposited in the same 

 order or proportions. Here is a perfect analogy, but 

 no identity ; and we can assign the reasons with the 

 greatest confidence, from knowing the various nature 

 of the substances deposited in them by the rivers, and 

 the unequal fertility of the organic beings which 

 they have nourished. In these deposits we find a 

 fair analogy, because in them we trace the germs of 

 the rocky strata. 



The uppermost of those deposits which are suffici- 

 ently antient to have assumed the character of rock, 

 are those known by the name of fresh water forma- 

 tions ; and these, it is probable, have been deposited 

 in the basins of antient lakes and aestuaries. Among 

 those that have hitherto been carefully examined, we 

 also trace similar analogies, but no identities. 



It is at a considerable distance from these, down- 

 wards in the order of the strata, that we find another 

 and a very important class of deposits, namely, the 

 coal strata. In these also there is a general analogy 

 throughout ; but, in no two do the substances occur 

 exactly in the same proportion or order ; while we 

 can here also assign the probable cause, by knowing 

 that they are deposits from fresh water, and therefore 

 probably formed in separate lakes. 



It is unnecessary to prolong this reasoning, as its 

 object must already be obvious. Whatever sea* 



