436 DESCRIPTIONS OF ROCKS. 
lar. d. Micaceous. e. Hydromicaceous ; it graduating at times into 
hydromica or mica slate. f. Feldspathic, sometimes porphyritic (the 
rock Arkose) ; this variety occurs north of Lenox, Mass., and when it 
loses its feldspar, it becomes cellular, like puhrstone Sith has been used 
for millstones. g. Gneissoid ; containing some mica and feldspar in 
layers, and so graduating toward gneiss. h. Andalusitic ; containing 
andalusite, as in Mt. Kearsarge (Hitchcock). i. Tourmalinic ; containing 
tourmaline, The vicinity of the great crystalline limestone formation 
of the Green Mountain region, in Western New England (in Vermont 
to the west of the principal ridge of the Green Mountains), includes 
strata of quartzyte of great thickness, and high summits in Benning- 
ton, and to the north, and also south, consist of it. In several places 
the quartzyte strata graduate into, and also alternate with, hydromica 
or mica slates, and in Massachusetts and Connecticut, with gneiss. 
Between Bernardston, Mass., and Vernon, Vt., quartzyte occurs in 
large beds, and also graduates into gneiss and hornblendic rocks. 
Quartzyte exists also in the central part of Southern New Hampshire, 
in the Archean area of Wisconsin, and in the Rocky Mountain region. 
j. Novaculitic-quartzyte, or Novaculyte (Whetstone). Novaculyte is only 
in part an extremely fine-grained siliceous rock. Of this nature is 
the variety from Whetstone or Hot Spring Ridge, in Arkansas. This 
ridge, 250 feet in height above the Hot Spring Valley, is made up of 
the beautiful rock, ‘‘ equal,” says D. D. Owen, ‘‘in whiteness, close- 
ness of texture, and subdued waxy lustre, to the most compact forms 
and whitest varieties of Carrara marble. Yet it belongs to the age of 
the millstone grit.” Dr. Owen supposed it to have received its impal- 
pable fineness through the action of the hot waters on sandstone. An 
analysis of the rock afforded him (Second Rep. Geol. Arkansas, 1860, 
p. 24), Silica 98-0, alumina 0°8, potash 06, soda 05, moisture, with 
traces of lime, magnesia and fluorine 0-1=100. He states that along 
the southern flank of the ridge there are over forty hot springs, having 
a temperature of 100° F. to 148° F. Solid masses from the fine rock 
have been got out weighing about 1,200 lbs.; the coarse varieties are 
made into stones for bench tools. 
2. Itacolumyte.—Schistose, consisting of quartz grains 
with some hydrous mica; on account of the mica in the 
lamination, it 1s sometimes flexible, and is called flexible 
sandstone. 
Occurs in the gold regions of North Carolina and Brazil, and dia- 
monds are supposed to be sometimes connected as to origin with this 
rock. 
3. Siliceous Slate.—Schistose, flinty, not distinctly granu- 
lar in texture. Sometimes passes into mica slate or schist. 
4. Chert—An impure flint or hornstone occurring in 
beds or nodules in some stratified rocks. It often resem- 
bles felsyte, but is infusible. Colors various. Sometimes 
odlitic. Kinds containing iron oxide graduate into jasper 
and clay ironstone ; and others, occurring as layers or no- 
