476 ON THE SUCCESSIVE FORMS 



the deposition of the secondary strata; and the lowest 

 is that at which this, the next subsequent series, or 

 any part of it, was elevated. It is therefore necessary 

 to ascertain the place of the next revolution which 

 followed the one which raised the primary strata ; and 

 this can be done, only by examining the whole of the 

 secondary, and by observing where the first indica- 

 tions of such a change occur. That it did not involve 

 all of these, as denoted by this general term, I hinted 

 before, and shall now attempt to prove; by showing 

 that the greater part of them were not in existence at 

 the time of the first elevation. 



We do not know the nature and number of the 

 unconformable strata which follow the primary in 

 every part of the world ; while I have also just shown, 

 as I have formerly proved by facts, that deficiencies 

 may occur, in such a manner as to permit, in one 

 place, an upper member or an upper series to come 

 into contact with a rock^ from which, in some other, 

 it is separated by a great number of intervening 

 strata. Thus, even strata high up in the secondary 

 series have been shown to come into contact with 

 gneiss and with granite. This fact therefore does not 

 affect the general reasonings that are to follow : in 

 some cases, it may show that certain revolutions were 

 partial : in others, it is explained by various circum- 

 stances already examined, such as^ the loss of pre-ex- 

 isting strata, and the effects of the elevating and dis- 

 turbing forces. It is sufficient, for the present pur- 

 pose, to assume the lowest secondary strata which 

 exist in any part of the world. If these should prove 

 very limited, it will follow that the revolution which 

 disturbed them was partial ; if widely diffused, that 

 it was more general, or perhaps universal. To sim- 

 plify this question, therefore, I shall take the lowest 



