On the Nor tan or "Upper Zanrentian " Formation. 285 



ing of the composition of these anorthosites is that the 



large fragments of crystals have a deep violet colour, 

 while the broken material is white. The contrast is 

 observed with especial distinctness on a weathered sur- 

 face or in a thin section nnder the microscope. The differ- 

 ence of the colour is due to the fact that the small 

 inclusions which abound in the large plagioclase indivi- 

 duals are wanting in the granulated portion of the rock. 

 They have evidently gathered themselves together into 

 small masses of titanic iron ore, which are enclosed in 

 the broken plagioclase, but are not found in the large 

 individuals. The contrast of these colours is so marked 

 that in a section containing plagioclase in both condi- 

 tions, we can predict at once nnder the microscope, from 

 the colour exhibited, how much of it is in a granulated 

 condition and how much is not, even before the structure 

 has been actually brought out by means of polarized light. 



This seems at first sight to point to a complete recrvs- 

 tallization of the granulated parts, but there are no facts 

 which make this probable, The feldspar does not change 

 its composition. In many sections we can actually 

 observe the origin of the fine grained material from the 

 outer portion of the larger individuals. This process 

 begins in an irregular extinction of a part of the periphery, 

 which is followed by the breaking off of the fragments. 

 It is also observed that so soon as a fragment is separated 

 from the larger mass it becomes colourless. It would 

 seem then, that the granulation in some way or another 

 gives free scope to the agent by which the accumulation 

 of the material of the small inclusions into the larger 

 masses is brought about. This question we shall consider 

 again in considering the anorthosites of the Sagnenav 

 liiver. 



Wherever we find an anorthosite, as in a portion of the 

 Morin area, which is composed entirely of finely granular 

 material, it can hardly be distinguished by its appearance 



