Ch. VII.] THE GRANITIC AND SCHISTOSE ROCKS. 137 



granite, where it forms a continuous bed over a very large 

 tract of country, with an elevation somewhat varying, and, 

 consequently, in an undulating plane : its dip is invariably 

 to the south, at an angle of from 5 to 50, and even to 60. 

 Tn one place, a considerable contortion of the bed occurs, 

 and in many others, fractures and dislocations of it may be 

 seen. " Yet, with such partial irregularity," observes Dr. 

 Macculloch, " we may still safely consider the general pa- 

 rallelism and stratification as regular, and the dip as a 

 medium constant quantity of, perhaps, twenty degrees." But 

 when the limestone is contiguous to the granite, it assumes, 

 with some few exceptions, a very different aspect. Its large- 

 grained and crystalline texture disappears, and it more nearly 

 resembles hornstone or compact felspar, having a smooth 

 texture, with a thin-edged fracture intermediate between the 

 splintery and flat conchoidal : it is very hard, effervesces 

 slowly with acids, and gives on analysis a large portion of 

 siliceous matter ; and its external aspect, where it has been 

 worn by the action of the river, is not much unlike that of 

 granite or porphyry. In every instance, all particular or 

 minute regularity disappears, wherever the limestone beds 

 are found in the immediate vicinity of the granite : they are 

 generally much contorted, and so intermingled and blended 

 with the accompanying strata, and with the granite, that the 

 whole mass appears to be in a state of utter confusion. 



The other strata, which accompany and alternate with the 

 limestone, are schist and quartz-rock, terms which have also 

 such an extensive signification, that it is absolutely necessary 

 to describe them at length. 



The schist of Glen Tilt rarely maintains the same cha- 

 racter for any considerable space : the most abundant is a 

 clay-slate, rarely fissile, and generally of a very compact 

 texture, and dark blackish-blue colour. It sometimes pos- 

 sesses a glossy and unctuous surface, and passes into a kind 

 of talcaceous schist. It is often much penetrated with quartz, 

 and sometimes finely interlaminated with the same substance : 



