MINERALOGY OF THE PENTLAN'D HILLS. 197 



that it is entirely of a chemical nature. Sometimes 

 it has still more of the fragmented appearance, 

 when it £oxm^ clay stone-tuff, a rock to be described 

 afterwards. It rests upon claystone-tuff ; is fre- 

 quently intermixed with it, aiid probably alter- 

 nates with it. It passes into porphyry, a rock 

 which rests upon it ; and is intimately related to 

 compact felspar, into which it passes, and in which 

 it is probably contained in beds. 



On the north-east, south, and south-west accli- 

 vities of Turnhouse Hill, where the line of junc- 

 tion can be discerned, it is to be observed resting 

 upon claystone-tuif, and as far as I could ascertain, 

 never below or alternating with the clinkstone- 

 porphyry. In this hill, ats line of junction with 

 the clinkstone varies much in height : in some 

 instances, as on the eastern, and north-eastern foot 

 of the hill, being almost washed by the Logan Wa- 

 ter ; but more frequently it is far above the level 

 of the river, several hundred feet above the bottom 

 of the valley. It occupies nearly the same general 

 high level in Caernethy and East Side Black Hill ; 

 and on the north side of East Side Black Hill, I saw 

 it resting on claystone-tuff, which appears to rest on 

 clinkstone-porphyry. From East Side Black Hill, 

 along the western or upper end of the valley of 

 Logan Water, it does not appear until we pass 

 Logan Water, vv'hen numerous fragments of it are 

 to be observed on the west side of the valley, lead- 

 ing from Habbie's How north-east towards Be- 

 Telaw, where it appears to be associated with cora- 



N 3 



