BY W. H. TWELVETREES AND W. F. PETTERD. 59 



the only direction in which the 001 imperfect cleavage lines 

 appeared the extinction ^Yas straight. No pleochroism is 

 perceptible. The mineral contains microscopical fluid in- 

 clusions with moving bubbles, some of which are easily 

 visible with a half -inch objective, other bubbles are 

 stationary. 



Another new mineral, which may be added to the list of 

 components of this singular rock, is the boro-calcium sili- 

 cate danburite, famous for its crystallographic resemblance 

 to topaz. It is disseminated through the stone and 

 abundant on fissure planes in glistening irregular crystal 

 aggregates, looking like quartz ; but with a hackly kind 

 of fracture. It is colourless to pale yellow. Under the 

 microscope the relief in Canada balsam is weak, a little less 

 than that of quartz. It gives allotriomorphic interlocking 

 granular sections like grains of a qiiartzite, and is of startling 

 limpidity. Its interference colour is low, not above the 

 yellow of the first order. Its only inclusions appear to be 

 needles of actinolite. 



On one of our slides we notice in the clear substance of 

 the axinite some pale green sub-spheroidal and polygonal 

 translucent crystals generally made up of rods or fibres 

 somew^hat curved, proceeding from the periphery' to the 

 interior. These remind one of the decomposition pro- 

 ducts of borocite called " parasite " by Volger ("), a 

 hydrous magnesian borate. The wavy fibres are suggestive 

 of some of the forms met with in precipitations from a 

 saturated solution, and the phenomena seem to point to 

 the existence of an excess of boric acid in the rock magma. 



As the serpentinous and gabbroid rocks at and to the 

 west of the Colebrook must be more ancient than the 

 Colebrook dyke, and if our interpretation be correct, also 

 older than the phrase of activity in the granite basin, it 

 follow^s that we have here some light thrown upon the 

 question of the age of the granite of the West Coast. We 

 do not now formulate a theory of its age, but simply 

 observe that the limurite rock will probably be found to 

 constitute one of the factors to be reckoned with in settling 

 that question. 



* Zirkel, Mik Besch, min und Gesteine 1878, p. 226. 



