236 ' AN ENQUIRY INTO THE [Ch. XII. 



bearing in Scotland, as in Cornwall, we should then learn 

 that regular parallel lines, having the same strike as the 

 schistose rocks, are more distinctly defined in the granite than 

 in the gneiss. 



But it has also been observed by Lyell, that " the analogy 

 between the primary slates and the acknowledged sedimentary 

 deposits, is not only shown by their beds being respectively 

 parallel with each other, but also by their being subject to 

 the same irregularities." 



On the same grounds it may also be maintained, that the 

 granitic rocks are also stratified; for, wherever a section of 

 granite is exposed which is not in the direction of its bearing, 

 that is, wherever the section is not confined to one and the 

 same layer, the seams of the rock will be found to describe 

 various irregular figures: sometimes the opposite lines are 

 widened, sometimes contracted, and, not unfrequently, they 

 terminate in a cuneiform mass by the union of these lines. 

 And when these irregularities occur, the different layers are 

 generally marked by a variation in the proportion and the 

 mode of aggregation of the constituent parts. In some of 

 these cases, it is true that most geologists would pronounce 

 these layers to be veins ; but, when layers of slate display 

 precisely the same phenomenon, they are never so designated. 

 A diagram illustrating these irregularities is given by Lyell ; 

 they appear -in the Pyrenees, in a coarse argillaceous schist, 

 and they are, as in the case of granite, accompanied by a 

 difference in composition, part of the rock approaching in 

 character to green and blue roofing slates, while another part 

 is extremely quartzose, the whole mass passing downwards 

 into mica-schist. 



It has already been stated (in the chapter on the structure 

 of the primary rocks), that whilst the common granite is either 

 divided by open seams, or may be cloven into quadrangular 

 blocks, the upper part of the quarries often exhibits various 

 curved lines developed by partial decomposition, as at Cam- 

 Gray near St. Austle, and at Kitt Hill near Callington. 



