138 POSITION AND NATURE OF [Ch. VII. 



at other times it is intermixed with hornblende, and passes 

 into hornblende schist: this occurrence is frequent at the 

 junction with granite, where also the schist, when merely 

 argillaceous, generally displays unusual hardness. Micaceous 

 schist also occurs, and, in general, it is characterised by the 

 predominance of the quartzose ingredient; and in this way it 

 passes into quartz-rock by insensible gradations. The dis- 

 position of the strata of schist is the same as that of the 

 limestone; and when these two rocks alternate together, the 

 limestone is often interfoliated with thin laminae of the schist, 

 in consequence of which they appear to graduate into each 

 other. These two rocks are not always regularly parallel 

 with each other. " Near Gow's Bridge, a white marble is 

 surmounted by a bed of hornblende schist ; this is followed 

 by marble about two feet in thickness, of which the greater 

 part is suddenly cut off at right angles to the bed by a second 

 mass of hornblende schist ; while the lower part continues in 

 the same direction, but bent, and of the breadth of only two 

 or three inches. The lower part of the mass of schist, which 

 thus intersects the marble, is also protracted in a thin plane, 

 continuous with the thin part of the marble, and lying above 

 it ; while the upper side of the same becomes continuous with 

 a regular and thick bed of the schist. A thick bed of marble 

 is therefore included on three sides within the hornblende 

 schist, its outer extremity being cut through at right angles 

 by the schist. As the beds dip into the hill, the further pro- 

 gress of this arrangement cannot be traced." 



The quartz-rock of the Tilt is similar to that generally 

 associated in Scotland with gneiss and mica-slate in the 

 vicinity of the granite. It is frequently of a bluish colour, 

 very uniform and compact, and approaching nearly to common 

 quartz in character, but still showing evident marks of 

 foliation. When it approaches the limestone and schist, with 

 which it alternates, all these rocks are found to pass gradually 

 into each other. 



This quartz-rock, however, very frequently contains felspar; 



