232 Tlie America?i Geologist. April, 1900 
the structure being allotriomorphic granular and the texture even and 
very fine. The constituent minerals are quartz and feldspar, the lat- 
ter chiefly orthoclase, although some grains are striated. The an- 
alysis, however, shows that these striated feldspars must also be alkali 
feldspars. The quartz grains are remarkable for having their inner 
parts densely crowded with opaque inclusions, apparently carbon- 
aceous, together with microlites in the form of prisms or rhombs. 
The outer rim of the grains is ordinarily clear. Accessory minerals 
are occasional zircon, actinolite, and magnetite showing alteration 
to rhombs of siderite. 
No. 4 is classified from its structure as an alaskyte porphyry. It 
occurs on Forty-mile creek as a silicious intrusion in a highly basic 
hornblende-epidote-pyrhrotite rock. It is light gray and resembles 
a quartzyte, except that the glimmer of large crystals of feldspar can 
be seen here and there. Under the microscope the phenocrysts are 
seen to be chiefly of orthoclase, although sometimes of orthoclase 
intergrown with a striated feldspar. The outlines of the phenocrysts 
are often ragged and imperfect. They are set in a groundmass con- 
sisting almost exclusively of fine-grained quartz, interlocking so that 
it has the exact appearance of a fine-grained quartzyte. Tiny flakes 
of biotite are abundant, both in the quartz groundmass and in the 
feldspar phenocrysts, and there is a little epidote. The comparatively 
low percentage of silica in the analysis comes from the large ortho- 
clase phenocrysts of the sample analyzed. 
No. 5 is classified as a tordrillyte on account of its fine-grained 
groundmass, and like No. i, it is a dike-rock from the Terra Cotta 
mountains. In the hand specimen the rock is nearly white, with 
small phenocrysts of quartz and feldspar. Under the microscope 
the quartz crystals are found to be in the form of dihexahedra, but 
their outlines show invasion by the groundmass. The feldspar 
phenocrysts were determined by the Fouque method to be ortho- 
clase, anorthoclase, and anorthoclase-albite, the latter two varieties 
being striated. The groundmass of the rock is a microfelsitic, some- 
times granophyric intergrowth of quartz and orthoclase. In the 
whole section the dark ferromagnesian silicates are almost entirely 
absent, only tiny quantities of secondary hornblende being found. 
Tonalyte group. — Tonalyte is adopted as a group name in- 
stead of quartz-dioryte, as being shorter and more characteriz- 
ing. In the same way, single characteristic names would be 
better for compound group names such as quartz-syenyte, oliv- 
ine-diabase, etc. In general, however, the system tends toward 
a great simplifying of rock names. 
Belugyte group.* — Under the belugitic family the only 
*The word belugyte is taken from the Beluga river in Alaska, in the 
neighborhood of which rocks belonging to the family were found. 
