6G //. F. Reid— Studies of Muir Glacier. 



between the hornblende individuals are filled with opaque white 

 feldspar. The hornblende surfaces are often seen to be poikilitic, 

 through a mottling with small idiomorphic feldspar crystals. 



Under the microscope the hornblende is brown and pleochroic 

 where freshest. It has the usual tendency to become green or 

 colorless wdiere it, has undergone incipient alteration. It is 

 closely associated with a quite abundant \yci\e greenish -gray 

 pyroxene. The two minerals are intimately intergrown, the 

 small areas of the hornblende in the pyroxene looking as though 

 they had resulted from the alteration of the latter mineral. A 

 narrow fringe of hornblende frequently surrounds the pyroxene, 

 while every grain of magnetite occurring in the pyroxene is 

 bordered by a deep green hornblende zone. The feldspar is basic 

 and much striated by tAvinning. It is also consideralily altered 

 to sericite and saussurite. 



Aiigite-mica-diorite. — This rock (number 3) has a much finer 

 grain than the preceding, and differs from it mineralogically in 

 containing a considerable proportion of biotite. As a consequence 

 of this the amount of its pyroxene is much less a,ncl occurs only 

 as occasional cores surviving in the center of large hornblende 

 individuals. The hornblende in this rock is full of inclusions 

 which are irregularly distributed, like Judd's " schillerization '' 

 j)roducts. 



Number 4 is a rock quite like the last, but which shows evi- 

 donce of intense dynamic action. It contains neither mica nor 

 pyroxene in the particular section examined. All the constitu- 

 ents show^ the effects of pressure. The feldspar especially is 

 bent, broken and dislocated, showing in a beautiful manner a 

 peripheral granulation of the fragments.'^^ 



Number 5 is another augite-b earing mica-diorite, Avhich, like 

 the last described specimen, shows the extreme effect of dynamic 

 action. Its feldspars are bent, broken and granulated, while its 

 pale-gray pyroxene is peripherally altered to a new green horn- 

 blende, as is the case in the Saxon gabbros and granulites de- 

 scribed by J. Lehmann.f Its mica scales are also greatly bent, 



" All of the four preceding rocks show a striking resemblance to the 

 diorites described by the writer from the Cortlandt series from near Peeks- 

 kill, on Hudson river, New York, in Am. .Tonrn. Sci., 3d ser., vol. xxxv, 

 1888, p. 440. 



t ITntersuchungen iiber die Entstehung der altkrystallinischen Schie- 

 fergesteine, Bonn, 1S84, pp. 193 and 230. 



