6 4 



but floats off masses of the altered rock which, in the form 

 of bands, streaks, and isolated shreds are seen thickly 

 scattered through the granite in the vicinity of the con- 

 tact, and which, while less abundant, are found throughout 

 practically the whole extent of this batholith. The 

 separate fragments of amphibolite, where completely 

 surrounded by the granite, while clearly nothing more 

 than masses of altered limestone, are rather harder and 

 more "granitized" in appearance than the amphibolite 

 which is still interstratified with the limestone, and the 

 fragments sometimes have somewhat flowing outlines as 

 if they had been subjected to a certain amount of movement 

 when in a softened condition. 



When examined in thin sections under the microscope 

 the limestone which is in the act of passing into amphi- 

 bolite is seen to do so by the development in it of certain 

 silicates. These, when the change is complete, are so 

 abundant that they entirely replace the calcite, while in 

 the intervening stages some of the original calcite still 

 remains. These silicates belong to the following species: 

 pyroxene, hornblende, sphene, scapolite, plagioclase, 

 microcline, orthoclase, and quartz. The relative abund- 

 ance of these minerals varies in different bands and from 

 place to place in the rock. Their characters are as 

 follows : 



The pyroxene is rather deep green in colour and 

 non-pleochroic. It is one of the chief constituents, being 

 present in large amount in the earlier stages of the change. 

 It first appears in rounded individuals which possess 

 neither crystallographic outlines nor any approximation 

 to crystalline form. In those varieties rich in calcite, the 

 sections of the pyroxene grains are frequently nearly 

 circular. 



The hornblende, which at first is much less abundant 

 than the pyroxene, is also green in colour, but it is a much 

 deeper green than the pyroxene. The grains are similar 

 to those of the pyroxene in form, but are usually less 

 rounded. It is intimately associated with the pyroxene, 

 often forming adjacent grains, but there is no conclusive 

 evidence that one mineral is derived from the other. It is 

 strongly pleochroic. 



The sphene is present only in very small amount in 

 the form of small rounded grains of brown colour. 



