. Annals of the New York Academy of Sciences. Science. 286 IRVING. spathic. In this are embedded phenocrysts, of plagioclase and quartz, with occasional sanidines. The groundmass contains scattered grains of magnetite. The plagioclases show an extinction angle on albite lamellae of 18 to 20 degrees, which show them to be of quite a basic type. They are sometimes seen in parallel growth with san- idine. In the only large sanidine crystal seen in the slide, a complete crystal of plagioclase was included. (Fig. 14.) The quartz is in extremely large crystals, and abounds in inclusions. It is resor
. Annals of the New York Academy of Sciences. Science. 286 IRVING. spathic. In this are embedded phenocrysts, of plagioclase and quartz, with occasional sanidines. The groundmass contains scattered grains of magnetite. The plagioclases show an extinction angle on albite lamellae of 18 to 20 degrees, which show them to be of quite a basic type. They are sometimes seen in parallel growth with san- idine. In the only large sanidine crystal seen in the slide, a complete crystal of plagioclase was included. (Fig. 14.) The quartz is in extremely large crystals, and abounds in inclusions. It is resorbed to a remarkable degree, the groundmass encroaching on it in unusually deep bottle- shaped cinbayvicnts. It is very much fractured, and frequently in long crys- tals that have a far greater lencrth than Plagioclase included in sanidine from quartz-asgerite-porphyry from sheet on Bur- lington and Missouri River Railroad, near Terry Station. 6. Diorite Family. Tonalite ( Quartz - mica hornblende - diorite ). —This rock is exposed in the cut of the Fremont, Elkhorn and Missouri Valley Railroad in Deadwood Gulch, some little distance west of Go-to-Hell Gulch, and is in an exceedingly thick dike in the Algonkian formation. Megascopic Characters.—The rock is gray, granular-looking and of an even texture, the constituent minerals being of such size as to be easily recognized without the aid of the microscope. Basic segregrations and angular inclusions of a basic character are very numerous. Microscopic Cliaracters.—Under the microscope we may rec-. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original New York Academy of Sciences. New York, New York Academy of Sciences
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