IN GLEN TILT. S21 



limestone begins to appear about ten yards from it. Soon af- 

 ter, the hank of the river turns to the westward, and exhibits 

 the outgoings of the limestone strata for about a hundred 

 yards. Their average stretch may be considered as about 

 N. 30' E., within 20" of the direction of the bank, and their 

 dip is to the south-east., at an angle vai-ying from 26" to 56". 

 On a close examination, some rapid inflexions may be obser- 

 ved', and among them, a small one is remarkable for setting the 

 planes of the strata at right angles to one another. This is in 

 ilie slope of the bank, near to where the limestone is first seen 

 below the quartz rock. 



44. Returning now to the large bed of quartz, we find next 

 to it, on the eastward, a rock composed of quartz and brown 

 felspar ; and this is succeeded by an aggregate of quartz, brown 

 felspar, and hornblende. The granular quartz is not bounded 

 on this side by any tabular face, or strata-seam ; and we had 

 reason to think, that the granular quartz passes into the quartz 

 and felspar, and that again into the compound of quartz, fel- 

 spar, and hornblende. Though the constituent parts of this 

 last rock are those of a sienite, the mass differs from sienite in 

 having them less perfectly crystallised, especially the horn- 

 blende. It may be considered as bearing the same relation to 

 sienite, which the gneiss, already described as having an unstra- 

 tified structure, does to granite, and pei'haps may with proprie- 

 ty be called Sienitic Gneiss. Some specimens of it effervesce 

 with muriatic acid. 



45. In the rock of quartz and felspar, and in that of quartz, 

 felspar, and hornblende, there are no marks of a stratified struc-* 

 ture, nor are there any of a formation in beds ; except that, on 

 the south side of the stream, the sienitic gneiss lies vei-y dis- 

 tinctly over, and conformable to, some strata that follow to the 

 eastward of it, and dip to the south. This circumstance, as well 



as 



