68 Dr. AfCuLLOCH's Additional Remarks on Glen Tilt. 



Felspar. — Crystallized felspar is sufficiently rare in Scotland to render any 

 notice of its localities desirable. It occurs in veins in micaceous schist on the 

 hills that form tlie southern boundary of Glen Tilt. The substances asso- 

 ciated with it in the same vein^ are quartz and crystallized mica ; the whole 

 forming- a sort of granite vein, all the ingredients of which are independently 

 crystallized. It is commonly white, occasionally with a very pale tint of flesh- 

 colour. Although the specimens are of considerable size and the crystals 

 numerous, they are not so well defined as to permit their forms to be easily 

 described. Among them I observed flat rhombs and prisms of various com- 

 plicated figures, rendered more so by numerous irregular truncations of their 

 summits, but very obscure, either from the manner of their adhesion, or from 

 their coalescence with others. Whatever interest the almost endless modifica- 

 tions of crystals may possess, I know not that there is any thing in this case, 

 more than in many others, deserving of minute details ; the more so that, with- 

 out figures, the descriptions of complicated geometric forms are scarcely to 

 be rendered intelligible. One of the specimens which I procured in this placCj 

 exhibited a rare, perhaps a singular, appearance. The interior of the crystals 

 was of the usual white colour, but the surface to the depth of a line or more 

 was of a clear dark brown, graduating into the white, but not from the effect 

 of decomposition. As the collection of crystals consisted only of the variously 

 facetted summits of prisms, in which trapezoidal and rhomboidal figures pre- 

 vailed, the specimen bore a strong resemblance to a mass of crystallized 

 garnet. 



Adularia. — This mineral is of still more rare occurrence in Scotland than 

 the preceding. The very small specimens which I procured, were found in 

 the same cavities with the felspar, and consisted of quadrangular prisms with 

 terminations variously and irregularly facetted. 



Garnet. — This mineral is so common in the schistose rocks of Scotland, 

 that it is almost unnecessary to mention it as found at this particular place. 

 It occurs both in the micaceous schist and in the hornblende schist ; in which 

 latter it is here very common, although by no means of very frequent occur- 

 rence in this rock in other situations. It is more worthy of remark, that it is 

 often of a very pale reddish-white colour and granular fracture, much resem- 

 bling certain varieties of granular quartz ; and that, in some cases, it is so like, 

 both in colour and texture, to the very compound schists in which it is imbed- 

 ded, that it would not be suspected to exist if it was not detected by the wrath- 



