TIREY. MINERALS. 53 



I must now proceed to describe at more length the 

 mineral substances contained in the rocks of Tirey ; the 

 most conspicuous of which are those at present ranked 

 under the general term of pyroxene. All these, as 

 must already have appeared, are contained in the 

 different limestones; the darker coloured, which possess 

 the characters of augit, being found in the pink lime- 

 stone, and the several varieties of sahlite in the white. 



I have pointed out in different parts of this book the 

 predominance of augit in Rum, in the Shiant isles, in Sky, 

 and in Arran ; it occurs also in other places, but always as 

 a constituent of the trap rocks. In Tirey alone, as far as 

 I have observed, it is found in primary limestone. Sahlite 

 is found in a more dispersed manner and in smaller 

 quantities ; but it occurs in several places, as in Harris 

 and in Glen Elg, affording different varieties, and gene- 

 rally, as it is here, accompanied by tremolite and forming 

 large nodules in primary limestone. In Rannoch I have 

 also found it imbedded in a primary micaceous limestone, 

 in distinct crystals, resembling those specimens found at 

 the Lake Baikal. In this place it is accompanied by 

 quartz, titanite, and oxidulous iron. In Glen Tilt it forms 

 distinct beds in the primary limestone, and in this situa- 

 tion also it is accompanied by tremolite. The augit 

 which occurs in the pink marble of Tirey sometimes pre- 

 sents large, distinct, imbedded crystals, an inch in length, 

 of a dark green or nearly black colour. These resist de- 

 composition longer than the limestone, and are conse- 

 quently found protruding from its surface when that has 

 been exposed to the weather. In some places it forms 

 shapeless masses, while in others it appears diffused 

 through and intimately mixed with the calcareous matter ; 

 in which case, like the distinct nodules, it is often attended 

 by an investing zone of greater hardness than the 

 general mass of the rock. But its most common ap- 

 pearance is that in which it is generally known as 

 forming a constituent part of the marble ; in this state 



