32 B. Silliman— Mineralogical Notes. 
demarcation, and the occurrence of dikes and allied features, 
show that the conditions of extreme metamorphism have 
probably been accompanied by a great softening of the rock, 
allowing ready molecular rearrangement into structureless 
forms, and producing plutonic and other appearances indicative 
of an exotic character. 
The same granite mass, approached from opposite sides, 
might convey entirely different impressions as to Its origin; a 
metamorphic indigenous nature being indicated upon the one 
hand ; an eruptive, exotic origin upon the other. 
oubt if any of the large granite masses of the mountains 
are of true intrusive character, and even if those smaller ones 
which are clearly intrusive have come from great distances 
below, or are other than of the same series of rocks melted by 
the heat accompanying the metamorphism of the mass. 
Along the south side of the map, and exposed by the cafion 
of the Boulder Creek, are massive gray granites, with but 
few points where any structure was observed. 
All along this half of the map the general strike is approxi- 
mately east and west, with a northern dip. This is the case 
also along its west border. Near the north and east sides, 
however, the dip is south, indicating a synclinal structure 
running through the middle of the eastern portion of the map. 
A horizon in which a definite schistose structure tends to 
occur is indicated by the dotted area running through the 
center of the map. me of the rocks here are distinct schists, 
on the map. Usually these form hills or ridges, and while 
some are quite long, the prophyry has apparently often found 
vent through less extended openings, now showing as sugar- 
loaf formed hills, without the direction of the dike being 
clearly indicated. Such forms are shown by a cross. The 
porphyries vary considerably in character, but no careful com- 
parative examination of them has as yet been made. Some 
* 
ee eee 
