Granites from British Columbia, etc. 357 



enclosing angular bits of quartz which were finally com- 

 pletely altered to soapstone. It was found, moreover, that 

 the process could be repeated artificially. By boiling 

 finely powdered rock crystal in a solution of carbonite of 

 potass and sulphate of magnesia, the quartz grains were 

 found to become corroded and converted along their outer 

 portions into a scaly aggregate, rich in magnesia, undecom- 

 posed by aqua regia, and having the optical properties of 

 talc. 



The development of andalusite and staurolite in contact 

 zones might in many cases also serve as an excellent example 

 of this mode of growth, since in many cases such slates 

 have not undergone complete re-crystallization. 



Lastly, there are the double zones of pyroxene and horn- 

 blende, which have been described as surrounding the 

 olivine where it would come in contact with the plagioclase 

 in so many gabbros from various parts of the world. If 

 these "rims" are really the result of dynamic action as has 

 frequently been asserted, they afford one of the best 

 instances of the growth of one mineral in another in a solid 

 rock, for here we have the hornblende in many cases 

 occurring in the most delicate acicular crystals, distinctly 

 growing out into the large unfractured plagioclase crystals 

 on all sides. In the norite from Lake St. John, 1 however, 

 where these zones are especially well developed and which 

 is the occurrence that I have been able to study most care- 

 fully, there is practically no evidence of great dynamic 

 action, and the zones seem to be due to the caustic action of 

 the molten magma before the solidification of the rock. 

 There is, however, one difference between occurrences 

 described in this paper and those described by Cross and 

 Weinschenk, namely, that in these Yukon rocks the minerals 

 in question penetrate and apparently grow into, not one 

 mineral but several minerals. 



This third hypothesis seems, therefore, to be the one 

 which best accounts for the very peculiar mode of occur- 



1 "On the presenoo of zones of certain Silioates about the Olivin ocourring in 

 Anorthosite rocks from the River Saguenay." American Naturalist, Nov., 1886. 



