C O L L, M I N E R A LS. 65 



with hornblende in such a manner that it is difficult to dis- 

 tinguish one ingredient from the other. This is particularly 

 the case where the specimens are broken by a cross fracture, 

 the micaceous ingredient being scarcely visible unless 

 when the rock is split in the direction of its laminae. 



It is hardly necessary to say that hornblende in a dis- 

 tinct state is also found in this gneiss, since it must 

 already have appeared from the description of that rock, 

 in which beds of hornblende schist and hornblende 

 rock are mentioned as occurring. This hornblende is black 

 and of the most usual aspect, and is occasionally found iia 

 the form of aggregated crystals of large size, offering a 

 beautiful variety for the collectors of mineral specimens. 



This mineral occurs also in Coll under a different aspect, 

 but much more rarely, "since I only observed it in the 

 neighbourhood of Ben Feoul. It is of a platy fracture 

 and bottle-green colour, with a lustre approaching to the 

 metallic, being little less splendent than hypersthene or 

 diallage, with the latter of which it may easily be con- 

 founded. I may add that similar specimens of hornblende 

 are occasionally found in mineral collections arranged 

 under this title. This substance is found entering into 

 the composition of a rock of which the other consti- 

 tuents are common black hornblende and black mica ; 

 being sometimes mixed throughout the mass, and at others 

 forming large and distinct concretions. At times also, 

 quartz as well as felspar enter into its composition, and the 

 compound presents in this way various specimens of con- 

 siderable beauty. The rock itself constitutes a bed alter- 

 nating with the ordinary gneiss. I may further add 

 to this enumeration of the varieties of hornblende, that 

 a lamellar and green kind much intermixed with pyrites 

 is found forming a rock in the same neighbourhood. 

 This variety does not possess the metallic lustre which 

 characterizes the former. 



Actinolite is also found in Coll. It is of a bright green 

 colour and of a lamellar structure, forming in some 



VOL. I. F 



