234 SYNOPSIS OF GNEISS. 



passing gradually into dark bottle green and thus forming 

 the prase of mineralogists ; the colour appearing to be 

 derived from the actinolite schist with which it was as- 

 sociated in the rock. 



Felspar. Gneiss appears to be the natural repository of 

 the principal varieties of this substance, which is some- 

 times, but not necessarily, connected with the granite veins. 



Oxidulous Iron. This occurs so abundantly at times as 

 to form a constituent part of the rock. 



Hornblende Occurs chiefly as a part of the alternating 

 beds of hornblende schist, but is occasionally found in 

 distinct concretions and in the form of perfect crystals. 



Fluor Spar Is not common, but occurs in the gneiss 

 of Sutherland, sometimes aggregated in lumps, at others 

 diffused throughout with the other ingredients. 



Zircon. I have also found this mineral in the gneiss of 

 Sutherland. 



Tourmalin. This seems to occur but seldom; the 

 crystals, though small, are in general extremely perfect. 



Epidote. This mineral occurs in the gneiss of Suther- 

 land, often in such abundance as to form a constituent of 

 the rock. 



Pyrites Is sometimes, but rarely, found dispersed ; and 

 commonly in those varieties that contain hornblende. 



Molybdena. This rare mineral is found in the gneiss 

 of Baffin's Three islands, dispersed in minute grains among 

 the other constituent parts. 



Many other minerals have been occasionally described 

 as found in gneiss, but the true repositories of these 

 are the granite veins : or, at least, sufficient care has not 

 been taken so to distinguish between the two cases, 

 as to admit of their being here enumerated. The pre- 

 ceding list includes those which I have observed in 

 the gneiss itself. 



