38 GEOLOGY OF THE LOTHIANS. 



rading agents. Every thing connected with the relations 

 of the two rocks testifies, that the red sandstone has been 

 quietly deposited on a most irregular surface, one presenting 

 numerous asperities and corresponding depressions. 



Having noticed the relations of the different stratified mas- 

 ses to each other, and their mineralogical characters, we shall 

 next, in the same way, describe those unstratified or ignige- 

 nous formations, which are so generally associated with 

 them. The rocks of this great natural family may be di- 

 vided under two heads, the Felspathic and the Augitic. 



FELSPATHIC ROCKS, INCLUDING PORPHYRY AND CLINKSTONE. 



Of this class of unstratified rocks it may be affirmed, that, 

 as a mass, it may be considered as composed entirely of 

 felspar in different states of crystallization, and associated 

 with various structures. Other minerals sometimes enter 

 into its composition, but these, if viewed on the large 

 scale, are to be considered only as of occasional occurrence. 

 The states in which the felspar presents itself, are all those 

 between that of a compact and an earthy mode of ar- 

 rangement, and when these exhibit a determinately ag- 

 gregated structure, they are porphyritic, amygdaloidal, or 

 both. Of the structures which cannot be shewn in hand 

 specimens, but are on a more or less colossal scale, the ta- 

 bular concretionary mode of disposition is the only one ex- 

 hibited by the felspar series of the Lothians, and of this in 

 the Bass and Traprain Law there are fine examples. These 

 tabular concretions, if examined in their relations to each 

 other, never present appearances which can in any way 

 justify the confusion of the tabular with the stratified struc- 

 ture. In the tabular structure, there is no perfect uni- 

 formity of direction, but within a limited extent the con- 

 cretions dip to all points, passing into an amorphous rock ; 



