KINDS OF ROOKS.. 44] 
This rock used to be called talcose slate, but, as first shown by Dr C. 
Dewey, it contains no tale. it includes Paropiite schist, Damourite 
slate and Sericite slate (Glane-Schiefer and Sericit-Cchiejer of the Ger- 
~mans. ) 
VARIETIES.—a. Ordinary ; more or less silvery in lustre. b. Chilo- 
vitic ; contains chlorite, or is mixed with chlorite slate, and has there- 
fore spots of olive-green color; graduates into chlorite slate. ¢. Gur- 
nN: tiferous. d. Pyritiferous ; contains pyrite in disseminated grains or 
crystals. e. Mugnetitic ; contains disseminated magnetite. f. Quart- 
zytic; consists largely of quartzyte, or is a quartzyte ‘rendered schistose 
and partly pearly by the presence of hydrous mica, as is well seen ina 
ridgé northeast of Rutland, Vermont, which consists partly of quartzyte 
and partly of hydromica schist. 
7. Paragonite Schist—Consists largely of the hydrous 
soda mica “called paragonite (p. 314); but in other characters 
resembles hydromica schist. Metamorphie. 
8. Minette.—Brown to black, fine-grained, compact, not 
distinctly schistose ; consisting of biotite ‘(according to 
the description and analysis of Delesse) and orthoclase ; 
contains also a little hornblende. Occurs in beds in the 
Vosges, France, associated with granite, syenyte, and other 
crystalline rocks. Sometimes feebly porphyritic and small- 
concretionary, the concretions consisting mainly of ortho- 
clase. Made eruptive by Delesse, and metamor phic by some 
later authors. Approaches argillyte in aspect. 
9. Greisen.— Massive, without schistose structure. A mix- 
ture of granular quartz and mica, in scales. ‘he mica may 
be muscovite, lepidolite, or biotite. It is a granite with the 
feldspar left out, and occurs in regions of gneiss, granite, 
or quartzyte, and sometimes graduates into these rocks. 
Metamorphic. 
Occurs in characteristic form at Zinnwald, in the Erzgebirgc, where 
it sometimes contains tin ore as an accessory ingredient, and is fre- 
quently penetrated by veins of tin; also in the tin ore regions of 
Schlackenwald and Cornwall. Occurs in the region of quartzyte, horn- 
blendic rocks and gneiss, of Upper Silurian age, between Bernards- 
ton. Mass , and Vernon, Vt., within three miles northeast of the former 
place, and aiso near Vernon ; but at this place it contains usually a 
little hornblende, making it a very tough rock, and is intermediate 
between the quartzyte, hornblendie rock and mica schist of the region. 
10. Mica-Argillyte or Mica-Phyllyte.—Includes the part of 
argillyte (p. 428) which has the composition nearly of a hy- 
drous mica, like that of the White Mountain Noth, where 
much of it is andalusitic. Analysis of this White Mountain 
rock, by Hawes, afforded Silica 46°01, alumina 30°56, iron 
sesquioxide 1°44, iron protoxide 6°85, manganese protoxide 
