478 ON THE SUCCESSIVE FORMS 



of England should he found widely diffused over the 

 globe, it would prove that this revolution had heen, 

 at least equally extensive. 



It must now however be observed, as before hinted, 

 that the secondary strata could not have been ele- 

 vated above the level of the waters without their 

 foundations ; and thus therefore the primary strata 

 are proved to have experienced two disturbances, at 

 least, up to the present point : two, if these revo- 

 lutions were general ; many, respecting which we can 

 form no conjecture, if they were partial and succes- 

 sive, or different in different places. And as the 

 period of repose of that world in which these lowest 

 secondary strata were formed, is measured by their 

 depth, it was apparently inferior in duration to thut 

 of the condition which preceded it ; as their greatest 

 or average dimensions do not appear to equal those 

 of the primary. 



At this point in the revolutions of the glohe, there 

 commences a very intricate set of changes, without 

 which it is impossible to explain the generation and 

 position of the coal strata. These occupy detached 

 places, reposing on the inferior rocks wherever they 

 happen to lie ; often, if not always, in an uncon- 

 formable position to those, and, frequently, very 

 much disturbed. They consist of various alternations 

 of sandstone, shale, clay, and coal, and occasionally 

 of limestone ; varying, almost every where, in num- 

 ber, in order of alternation, in the proportions of the 

 several substances, and in the total depth of the whole 

 deposits. We have no reason to think that they are 

 the produce of different seras, if they do not always 

 lie on the same rocks ; for the reasons already stated: 

 there is, on the contrary, some reason to think, but 

 no proof, that they are the produce of the same ; be- 



