KOCKS : THEIR CONSTITUENTS AND KINDS. 87 



rhyolyte. From Eureka, Nev., and other parts of the Rocky Mountain region ; also from 

 the Andes of Cotopaxi, Chimborazo, etc. 



Propylyte is altered andesyte. 



AuGiTE-ANDESTTE. — Eruptivc. Like andesyte, but containing augite in place of 

 hornblende, or in part hypersthenic ; augite or hypersthene often altered to hornblende, 

 often chrysolitic. Texture, crystalline -gi-anular to aphanitic and fluidal and glassy. 

 Reported from the Great Basin. A chrysolitic variety is one of the rocks that have been 

 called melaphyre. 



Htpersthexe-axdesyte. — Eruptive. Like the preceding, but containing hyper- 

 sthene in place of augite or hornblende. Buffalo Peaks, Col.; Mount Shasta, etc. 



Htperyte (A^07'?/«e in part. Hyper sthene-gahbro). — Consists chiefly of labradorite 

 or anorthite and hypersthene, with usually some pyroxene, biotite, and magnetite, and 

 sometimes chiysolitic. Occurs west and northwest of Baltimore, Md. ; in the Hartz, 

 Norway, etc. 



Gabbko. — Eruptive, metamorphic, granitoid. Consisting, like the following, chiefly 

 of labradorite and pyroxene, the latter often a foliaceous (diallagic) variety ; some horn- 

 blende often present, also magnetite and ilmenite ; sometimes chrysolite, which is often 

 changed to serpentine. Color, dull grayish, flesh-red to brownish and gray. G = 2-7-3*l, 

 least when the proportion of pyroxene is small. Quartz-gabhro, containing disseminated 

 quartz, occurs in northeastern Maryland and northern Delaware. 



The name gabbro is of Italian origin ; but it is used in Italy, as it has long been, for a 

 green serpentine rock. And gabbro-rosso is a red altered variety of the same. 



DoLERYTE {Trap). — Eruptive. Texture varying from granitoid to aphanitic and 

 glassy, scoriaceous and volcanic. Consists of labradorite and pyroxene, the latter some- 

 times foliaceous. A kind found at Lassens Peak contains much quartz in disseminated 

 grains, and is a quartz-doleryte (Diller). G = 2-8-3-1. Color, dark gray to grayish black, 

 greenish black, and brownish to black. Structure frequently columnar, often chrysolitic. 

 Chrysolitic kind sometimes altered to impure serpentine. Ordinary trap often altered 

 to a hydrous, chloritic trap, often also amygdaloidal, with feeble luster and of easy 

 decomposition. Includes three sections : (1) Diabase., containing no glass in the base 

 and no chrysolite. (2) Dolenjte, containing glass in the base, but no chrysolite. 

 (3) Basalt., containing usually more or less glass, also chrysolite. 



The t7-ap of the Palisades, Connecticut River, and other parts of the Triassic of 

 eastern North America belongs here, and much of that of the copper region of Lake 

 Superior. There is a fine exhibition of columnar trap at Orange, N. J. (Fig. 221, page 262). 

 The name melaphyre has sometimes been used for chloritic trap. Diabase-schist is a slaty 

 form of diabase, probably metamorphic. 



Tachylyte. — Eruptive. A black basalt-glass, found in connection with basalt lavas. 



Camptonyte. — Rock resembling diabase and doleryte. Consisting of hornblende 

 (as an original mineral of the rock) and probably anorthite, the analysis affording only 

 41 to 44 per cent of silica (Hawes, 1876 ; Kemp, 1889). From Campton Falls, N.H., and 

 near Whitehall, N.Y. 



Ettceyte. — Eruptive. A doleryte-like rock, consisting chiefly of anorthite and augite, 

 with sometimes chrysolite. Granitoid to aphanitic, and as a lava. Elfdalen, Norway ; 

 Puy de Dome, France ; etc. 



CoESYTE {Orbicular Dioryte). — Eruptive. Consists of anorthite and hornblende, 

 with some quartz and biotite. Contains large concretions consisting of anorthite and 

 hornblende, with some quartz. Corsica ; the Shetlands, etc. 



Anorthityte {Anorthite Bock of Irving). — Eruptive. Crystalline granular. Con- 

 sists largely of anorthite, or a feldspar near it in composition, and is of a light gray color 

 to white or faintly greenish. North shore of Lake Superior, between Split Rock River 

 and the Great Palisades, and in Carltons Peak, near the mouth of Temperance River. 



Nephelinyte {Nepheline-doleryte, Tephryte^. — Nephelite and augite, with some 



