80 ON THE CONVOLUTIONS OF STRATA, 



and history ; so that observations made at any one part of the 

 range, may, with confidence, be applied to the rest. 



• There are but few exceptions to this general rule, which 

 have come to my knowledge. At the Rae Quarry in Peebles- 

 shire, near the Crook Inn, a Limestone containing shells oc- 

 curs, interstratified with killas ; and in the stewartry of Kirk- 

 cudbright, there are three Granitic districts in the midst of this 

 rock, whose relations with it exhibit some interesting facts, 

 which will occupy the second part of this paper. A granite 

 mass also occurs within the range of this same mass of killas, 

 at Priestlaw on the Water of Fasnet, in the mountainous part 

 of East Lothian. 



The killas consists everywhere of an assemblage of strata of 

 various thickness, from several yards to the minutest leaf of 

 slate. It is in general of a dark-blue colour, and, when exa- 

 mined, is found to consist of a congeries of fragments, which 

 bear the most undoubted proofs of having been deposited in 

 an horizontal position. The strata lie parallel to each other, 

 but are everywhere far from being horizontal, their pre- 

 vailing and best known position being vertical, or nearly 

 so. They are often bent, however, at various angles, fre- 

 quently very acute, and sometimes with the strata nearly 

 doubled upon themselves. In all the inland part of this 

 range, the rock appears so partially, shewing itself only in ri- 

 ver-courses, or in quarries, that it is difficult to obtain any 

 correct information as to the position of the strata, which fre- 

 quently exhibit great seeming irregularity, and which cannot 

 be described, without making use of language which at first 

 sight bears an appearance of contradiction in terms. Thus 

 it not unfrequently happens, that one set shews itself in 

 a position, at the surface, nearly erect, but having a decided 

 dip to the east ; and that in the immediate neighbourhood, 



another 



