378 
The American Geologist. 
June, 1896 
Quartz-diorite Family, —oligoclase-andesine feldspars and quartz. 
Quartz-diorite, —structure hypidiomorphic or granitic. 
Quartz-diorite-porphyry ,—structure porphyritic. 
Dacite, —structure microlitic or glassy. 
Syenite Family, —alkali feldspar. 
Syenite ,—structure granular. 
Hornblende-syenite. 
Mica-syenite. 
Augite-syenite. 
Syenite-porphyry ,—structure porphyritic. 
Trachyte ,—structure microlitic, or glassy. 
Diorite Family, — oligoclase-andesine feldspars. 
Diorite ,—structure granular. 
Hornblende-diorite. 
Mica-diorite. 
Augite-diorite. 
Diorite-porphyry ,—structure porphyritic. 
Andesite ,—structure microlitic or glassy. 
Gabbro Family,— labradorite-anorthite feldspars. 
Gabbro ,—structure, granular or poikilitic. 
Hornblende-gabbro. 
Pyroxene-gabbro. 
Mica-gabbro. 
Diabase ,—structure diabase-granular, often ophitic. 
Hornblende-diabase. 
Pyroxene-diabase. 
Basalt ,—structure microlitic or glassy. 
Olivine-free basalt=labradorite, Levy. 
Olivine-basalt. 
Pyroxenite-peridotite Family,— proxene and olivine. 
Only one of the rock families noted above, that of the 
syenites, will be further treated in the present paper. 
Syenite Family. 
The family of syenites may be designated as that group of 
igneous rocks composed chiefly of alkali feldspars, that is to 
say, orthoclase, microcline, anorthoclase and albite. Quartz 
and soda-lime feldspars are often present in small amount, 
and there are usually ferromagriesian elements present and 
these are conveniently used for a further subdivision of the 
family. 
The group may be divided into three general classes accord¬ 
ing to the structure and degree of crystallization. 
Syenites proper —structure granular. 
Soda-syenite or albitite—all albite. 
Augite-syenite,—alkali feldspar and augite. 
Hornblende-syenite,—alkali feldspar and hornblende. 
Mica-syenite,—alkali feldspar and mica. 
Syenite porphyry ,—chiefly dike rocks, with porphyritic crystals in 
fine holocrystalline ground mass of alkali feldspar, etc. 
Trachytes and apo-trachytes, —chiefly surface flows. Structure 
microlitic and glassy. 
The apo-trachytes will include the orthophyres and kerato- 
phyres of the paleo-volcanic series of Rosenbusch and Michel 
