Geology of the Highlands. 233 



ing to the Wernerian arrangement. It would rather ap- 

 pear as if the gneiss rocks, ten miles in breadth, were the 

 central or oldest formation ; and that, beginning with this 

 rock, we could trace corresponding strata on each side. 



After this general view of the rocks constituting the 

 Highlands, a more particular account will be readily com- 

 prehended. 



The granitic layers embraced in the gneiss consist chief- 

 ly of no small proportion of semi-transparent quartz of a 

 hyaline appearance, a very little silver-coloured mica, and 

 a large proportion of greyish-white feldspar of a pearly lus- 

 tre. In a few limited localities the feldspar is flesh-colour- 

 ed. Sometimes the quartz is very dark coloured ; and in 

 some rocks the feldspar appears of a sky-blue colour. 



The mica of the gneiss is almost invariably black, and 

 the feldspar white. Beds of considerable extent are em- 

 braced in the gneiss rock near Fort Putnam, which consist 

 chiefly of hornblende. In this rock are found imperfect 

 crystals of green augite of a large size, and considerable 

 quantities of the green coccolite variety. 



Where the gneiss meets the hornblende rock stratum, 

 both north and south, many interesting minerals are dis- 

 seminated. The most beautiful specimens of serpentine in 

 calc spar are found at this meeting of the strata, three miles 

 north of the military academy. They appear like grass- 

 green gems set in masses of pearl. 



Vast quantities of very dark lamellar hornblende appear 

 in the form of veins traversing the hornblende rocks. The 

 same variety of hornblende is disseminated in the granitic 

 layers included in the gneiss rocks ; which is often mistaken 

 tor shorl on a slight view of the rocks. It sometimes gives 

 the granite a graphic appearance. 



Those geologists, who study hand specimens in the cabi- 

 net and are disposed to multiply names, may here find the 

 primitive trap, primitive greenstone, sienite, greenstone 

 porphyry ; and perhaps every other variety into which the 

 hornblende rock is varied in any country. 



The granulated iron ore containing small crystals of phos- 

 phate of lime which abounds in the gneiss rocks of these 

 mountains, together with the carburet of iron, with other 

 minerals, have already been mentioned in former publica- 

 tions. The minerals of these mountains, however, have 



