590 METAMORPHIC EOCKS. [Ch. XXXV. 



Explanation of the Names, Synonyms, and Mineral Composition of the 

 more abundant Metamorphic Hocks. 



Actinolite-schist. A slaty foliated rock, composed chiefly of actinolite (an emer- 

 ald-green mineral, allied to hornblende), with some admixture of garnet, 

 mica, and quartz. 



Ampelite. Aluminous slate (Brongniart) ; occurs both in the metamorphic and 

 fossiliferous series. 



Amphibolite. Hornblende rock, which see. 



Argillaceous-schist, or Clay-slate. See p. 589. 



Arkose. Name given by Brongniart to a compound of the same materials as 

 granite, which it often resembles closely. It is found at the junction of 

 granite with formations of different agea, and consists of crystals of felspar, 

 quartz, and sometimes mica, which, after separation from their original 

 matrix by disintegration, have been reunited by a siliceous or quartzose 

 cement. It is often penetrated by quartz veins. 



Chiastolite-slate scarcely differs from clay-slate, but includes numerous crystals 

 of Chiastolite : in considerable thickness in Cumberland. Chiastolite occurs 

 in long tlender rhomboidal crystals. For composition, see Table, p. 475. 



Chloeite-schist. A green slaty rock, in which chlorite, a green scaly mineral, is 

 abundant. See p. 589. 



Clay-slate or Argillaceous-schist. See p. 589. 



Eurite has been already mentioned as a plutonic rock (p. 564), but occurs also 

 with precisely the same composition in beds subordinate to gneiss or mica- 

 slate. 



Gneiss. A stratified or foliated rock ; has the same composition as granite. See 

 p. 589. 



Hornblende Rock, or Amphibolite. See above, p. 473. A member both of the 

 volcanic and metamorphic series. Agrees in composition with hornblende- 

 schist, but is not fissile. 



Hornblende-schist, or slate. Composed of hornblende and felspar. See p. 589. 



Hornblexdic or Syenitic Gneiss. Composed of felspar, quartz, and hornblende. 



Hypogene Limestone. See p. 589. 



Marble. See pp. 12 <fe 589. 



Mica-schist, or Micaceous-schist. A slaty rock, composed of mica and quartz, in 



variable proportions. See p. 589. 

 Mica-slate. See Mica-schist, p. 589. 



Phyllade. DAubuisson's term for clay-slate, from <pv\\as, a heap of leaves. 



Primary Limestone. See Hypogene Limestone, p. 589. 



Protoglne. See Talcose-gneiss, p. 5S8; when unstratified it is Talcose-granite. 



Quaktz Rock, or Quaetzite. A stratified rock ; an aggregate of grains of quartz. 

 See p. 5S9. 



Serpentine has already been described (p. 474), because it occurs in both divi- 

 sions of the hypogene series, as a stratified or unstratified rock 



Talcose-gneiss. Same composition as talcose-granite or protogine, but stratified 

 or foliated. See p. 588. 



Talcose-schist consists chiefly of talc, or of talc and quartz, or of talc and fel- 

 spar, and has a texture something like that of clay-slate. 



