National Geographic : 1892 Mar 21
H. 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 where it has undergone incipient alteration. It is closely associated with a quite abundant pale 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 twinning. It is also considerably altered to sericite and saussurite. Augite-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 and 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" products. 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-bearing mica-diorite, which, 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.t 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. Journ. Sci., 3d ser., vol. xxxv, 1888, p. 440. t Untersuchungen fiber die Entstehung der altkrystallinischen Schie fergesteine, Bonn, 1884, pp. 193 and 230.
1892 May 15
1892 Feb 19