KINDS OF ROCKS. 71 



a. Felsytes. 



(1.) Orthoclase-felsyte. — Color, whitish, greenish; lustre somewhat waxy, dull; 

 specific gravity, 2 '6-2 7. A greenish-gray specimen from Brittany consists of ortho- 

 clase and some quartz. 



(2. ) Albite-felsyte. — Similar to the preceding. A variety from Orf ord, Canada, 

 afforded T. S. Hunt (Logan's Report for 1853-56) — Silica 78-55, alumina 11-81, soda 

 4-42, potash 1-93, lime 0-84, magnesia 0-77, protoxyd of iron 0-72, loss by ignition 

 0-90 = 99-94. 



(3.) Diokyte-felsyte. — Compact diorite, and consisting, therefore, of albite or 

 oligoclase and hornblende. Color, grayish white, greenish white. Occurs in Orford, 

 Canada (T. S. Hunt, Logan's Report, 1853-56). 



(4.) Gabnet-felsyte. — A pure, compact, garnet rock of a whitish color, with 

 spots of disseminated serpentine. Specific gravity, 3-3-3-5. Exceedingly hard and 

 tough. Graduates into garnet-euphotide. Occurs at Orford and St. Francois, Canada 

 (Himt). 



b. Porphyroid Rocks. 



1. Common Feldspar-porphyry, or Orthophyre. — Consists of a base of ortho- 

 clase-felsyte, red, brown, or whitish in color, and much like jasper in lustre and fracture, 

 with disseminated crystals of orthoclase. 



-2. Elvaxyte, or Quartz-porphyry. — Gray, bluish-gray to brown and red, in 

 color of base. This base a felsyte, consisting of a feldspar with, usually, quartz, and con- 

 taining disseminated grains or crystals of quartz and feldspar. The feldspar is some- 

 times oligoclase. The crystals of feldspar are sometimes wanting. Some compact 

 slate-rock has the same composition. 



3. Porphyritic Diabasyte. — The antique green porphyry of Greece (southern 

 Morea) is here included. Specific gravity, 2-91-2-932. Color, dark green; dissemi- 

 nated feldspar crystals, large, greenish white. Composition of the base: silica 53-55, 

 alumina 19-43, protoxyd of iron 7-55, protoxyd of manganese 0-85, lime 8-02, mag- 

 nesia and alkali, 7-93, water, 2-67. The iron and magnesia indicate the presence of 

 hornblende or pyroxene. 



Porcelanyte, or Porcelain-Jasper. — A baked clay, having the fracture of flint and a 

 gray to red color: it is somewhat fusible before the blowpipe, and thus differs from 

 jasper. Formed by the baking of clay-beds when they consist largely of feldspar. 

 Such clay-beds are sometimes baked to a distance of thirty or forty rods from a trap 

 dike. 



Other porphyries are the porphyritic varieties of granyte, gneiss, dioryte, doleryte, 

 basalt, trachyte ; they are sometimes badly named granyte-porpliyry, dioryte-por- 

 phyry, etc. ; they are simply varieties of other species, characterized by having the feld- 

 spar in distinct crystals, a distinction of small geological importance. 



c. Euphotides. 



(1.) Feldspar-Euphotide. — Tough, compact, light green or grayish, consisting of 

 a minutely-granular feldspathic base with disseminated diallage or smaragdite. 



(2.) Epidote-Euphotide. — Similar to the preceding, but more tough, and heavy. 

 Specific gravity, 3-1-3-4. The base a compact whitish epidote (called hitherto saus- 

 surite), according to T. S. Hunt. From the Alps. Gabbro, in part. 



(3) Eclogyte, or Garn*et-Euphotide. — Either whitish, greenish, or reddish; very 

 tough and heavy. Specific gravity, 3 "2-3 -5. The eclogyte of Europe contains grass- 

 green smaragdite in a reddish garnet base. A related rock from Canada, according to 

 T. S. Hunt (Logan's Report for 1853-56, p. 450), contains grayish cleavable hornblende 

 or pyroxene, in a whitish or yellowish base. 



4. Chrysolite {or Olivine) Hocks. 

 Dunyte consists of granular chrysolite, and occurs with serpentine in Mt. Dun, New 



