various parts of Scotland. S99 



that the habits of this rock, and its connections, in all the cases 

 where I have had an opportunity of seeing it, seem to point it out 

 as an argillaceous schist, altered and indurated in consequence of its 

 proximity to greenstone. 



The last bed is the immense mass of columnar trap already men- 

 tioried, which surmounts the whole. The character of this rock is 

 not that of a greenstone, to use the word in its more restrained 

 sense, as it does not contain distinct grains of hornblende and 

 felspar, but is an obscure mixture of hornblende, felspar, and 

 quartz. 



I have therefore both here and in other places, (where I have had 

 occasion to describe the varieties of this rock, of which the charac- 

 ters are not so decided as to admit of their being placed either under 

 the heads of basalt, wacke, or greenstone,) preferred the general 

 name of trap to the use of a specific one with which the characters 

 of the individual cannot be made to agree. In so doing I have left 

 out of view the confusion which must arise if the siliceous schist, 

 and Lydian stone, which appear to be the trap of some authors, be 

 considered as forming a part of this great natural division, and have 

 taken the term, as I imagine, in the sense intended by the followers 

 of Werner. It is thus used by them as the title of a family^ in- 

 cluding basalt, wacke, greenstone, and clinkstone, a family well 

 expressed by the vernacular term whin., now, I believe, and perhaps, 

 unfortunately, obsolete. The characters of basalt, wacke, green- 

 stone, and clinkstone, are tolerably decided, and the geological 

 relations of the trap family are so remarkable that we ought to find 

 little difficulty in assigning proper terms of distinction to its respec- 

 tive members. But, independently of these four well characterized 

 rocks, innumerable varieties occur not properly referable to either, 

 and which cannot even be truly expressed without nmch circumlo- 



