8 GEOLOGY OF THE LOTHIANS. 



same as occurring in England ; these differences are, 

 however, only such as might be expected to be observ- 

 able in a deposit extending over a large area: one part 

 of a formation may be more fully developed in one si- 

 tuation than in another, or it may even be entirely awant- 

 ing. In regard to the mutual associations of the Augitic 

 and Felspathic masses, we may remark that, although no natu- 

 ral sections exhibit the relative ages of these rocks ; still, from 

 the examination of other districts, which are partially com- 

 posed of both ; from the circumstance of the trap family be- 

 ing so generally distributed among the carboniferous strata, 

 and also from the eruptions of the trachytes (which may be 

 considered as the modern analogues of the aneient porphy- 

 ries and felspars), being, in general, anterior to those of rocks 

 having a basaltic character, it is highly probable that the 

 series of felspar masses, which is so generally associated with 

 the Transition deposits, is of a formation more ancient than 

 the basalts and greenstones. In the three counties the geo- 

 gnostical structure of which it is the subject of this paper to 

 describe, extensive districts of both Transition and Secondary 

 strata occur, and, as we have just stated, the higher grounds 

 are composed almost entirely of the older rocks. Before 

 entering upon a minute topographical description of these 

 two great classes, and also before we define their geogra- 

 phical distribution, we shall describe both in a general man- 

 ner ; and as in all geognostical descriptions, it appears to be 

 most natural to follow the ascending series, so here we shall 

 first notice the 



TRANSITION ROCKS. 



To classify, according to nature, the various mineral masses 

 which constitute the crust of our globe, has been the endea- 

 vour of geologists, from that epoch in the history of the sci- 

 ence when it was first discovered, that, to arrive at the know- 



