236 



University of California Publications. 



[Geology 



proximity to the sedimentary mass. The hornblende resumed 

 the ordinary hypidiomorphie form, the quartz content was noted 

 to increase, and at the contact the rock had become a quartzose 

 granitite, barren of hornblende. Yet observation showed that 

 most frequently this particular variety of granite would pre- 

 serve its porphyritic habit to within two feet of the contact, 

 where it would become obliterated, and a slight enrichment in 

 the biotite content take place at the expense of the hornblende. 

 Tins tendency toward the formation of a narrow peripheral zone 

 relatively richer in biotite can macroscopically be seen to have 

 been operative at numerous points, and even appears from 

 microscopic evidence to have been effective in the leucoeratic 

 granites upon the eastern side of the area. 



Inclusions in the Granites. — Dark circular and irregular oval 

 patches, varying in size from half a square inch to a square 

 yard, are exceedingly abundant in the granites of the region. 

 They are resistant to atmospheric agencies and weather out in 

 relief. Their outlines are sharp and distinct, though in detail 

 interlocking with the grain of their hosts. The term "schliere" 

 when applied to these is a misnomer. On the basis" of textural 

 differences, two classes can be recognized : the first of which is 

 accurately described as a pepper-and-salt mixture of the dark 

 and light colored constituents; the second type is a dark colored, 

 medium granular aggregate in which occasional porphyritic feld- 

 spars are included. 



The distribution of these two varieties of inclusions is not 

 limited to any particular facies of granite, and is in general 

 fairly uniform throughout the region. Over wide areas a com- 

 mon perpendicular orientation of the major axes is often ob- 

 servable though the porphyritic hornblendes of the enclosing 

 rock are without definite disposition, either fluidal or gravita- 

 tional. 



At Eagle Lake, the glaciation has laid bare a truly remark- 

 able phenomenon. Here the granite abuts against a white, 

 schistose quartzite, which thermal metamorphism has rendered 

 massive and vitreous over a breadth of a few inches from the 

 irruptive. Paralleling the contact, and forming a zone in the 



