EOCKS : THEIR CONSTITUENTS AND KINDS. 85 



2. Potash-feldspar and Hornblende or Pyroxene Series. 



Stentte (Syenite of Werner). — Eruptive, metamorpliic ; granite-like, coarse to fine. 

 Gray to flesh-red and darli gray. Consists of ortlioclase, with often microcline and 

 hornblende and little or no quartz ; biotite and oligoclase often present. G = 2-7-2 -9. 

 From Plauen-Grund, Saxony, etc. Nearly all American syenyte is quartz-syenyte. 



QtTARTz-STENYTE (syenite of most early geologists, hornblende-granite, syenite-granite), 

 — Eruptive and metamorphic. Like syenyte, but containing quartz. Silica 70 to 80 per 

 cent. The name syenite is from Syene in Egypt, where a red granite graduating into 

 quartz-syenyte occurs, and is the material used by the ancient Egyptians for the exterior 

 lining of obelisks, etc. 



Syenyte-gneiss. — Metamorphic, eruptive. Like gneiss in aspect and schistose struc- 

 ture, and also in constitution, except that hornblende replaces mica. Common in Archaean 

 regions, as the New Jersey Highlands, the Adirondacks, etc. Graduates into Hornblende- 

 schist, a schistose rock consisting chiefly of hornblende. 



Augite-syenyte. — Eruptive. Like syenyte, but containing, with the orthoclase, 

 pyroxene in place of hornblende. A kind free from quartz occurs at Jackson, N.H. ; in 

 southern Norway. Monzonyte is stated to be a variety of augite-syenyte. 



AuGiTE-QUAETz-SYENYTE (Augite-gramte). — Metamorphic; igneous. Like the pre- 

 ceding, but containing quartz ; the augite in part altered to hornblende, and thence in all 

 stages of gradation down to a hornblende-syenyte. The gneissic variety is common in 

 Wisconsin, much more so than the granitoid. 



Unakyte. — A flesh-colored, granitoid rock consisting of orthoclase, quartz, and epi- 

 dote. From the Unaka Mountains, Madison County, N.C., and Cooke County, E. Tenn. 



3. Potash-feldspar and Nephelite Rocks, Hornhlendic or not. 



ZiRCox-SYENYTE. — Like syenyte. A crystalline granular rock consisting of ortho- 

 clase, microcline, elseolite, little hornblende, crystals of zircon ; often also sodalite, segyrite, 

 eudialyte, etc. From Norway ; Marblehead Peninsula, Mass., containing sodalite. 



FoYAYTE. — Eruptive. Coarse, crystalline granular to aphanitic. Consists of ortho- 

 clase, nephelite, hornblende, or fegyrite, with often sodalite, etc. From Mounts Foya and 

 Picota in Portugal, making a dike ; on eastern slope of Blue Mountain, New Jersey, 

 between Beemersville and Liberty ville. 



MiAscYTE. — Granitoid to schistose. Consists of microcline, elfeolite, biotite, with 

 some quartz ; often also zircon, monazite, sodalite, cancrinite, etc. From Miask, Ilmen 

 Mountains ; Pic Island, Lake Superior ; Litchfield, Maine. 



DiTKOY-TE. — Coarse to fine-grained. Consists of microcline, nephelite (elseolite), 

 and sodalite. From Ditro, Transylvania. 



Phonolyte (Clinkstone). — Eruptive. Compact, more or less slaty in structure. 

 Gray, grayish blue, brownish. Usually clinking under the hammer like metal when struck 

 (and thence the name). G = 2 •4-2-7. Consists of glassy orthoclase, with nephelite and 

 some hornblende. In Colorado, Auvergne, Breisgau, Bohemia. 



4. Leucite Rocks, with or without Augite. 



Usually some sanidin (orthoclase) is present, and often also nephelite and labradorite. 



Amphigenyte (Leucitophyre) . — Eruptive. Contains augite, like doleryte, but leucite 

 (called sometimes amphigene) replaces the feldspar. Often contains chrysolite, nephelite, 

 sanidin, labradorite, brown mica, with sodalite, etc. Dark gray, fine-grained, and more 

 or less cellular to scoriaceous. G 2-5-2-9. The leucite is disseminated in grains or in 

 24-faced crystals. Constitutes the lavas of Vesuvius and some other regions. 



Leucotephryte. — Erviptive. Like the above, and occurring in the same regions, 

 but containing much labradorite. 



