436 DESCRIPTIONS OF ROCKS. 



lar. d. Micaceous, e. Hydromicaceous ; it graduating at times into 

 hydromica or mica slate, f. Feldspathic, sometimes porphyritic (the 

 rock ArJcose), or like granulite in its disseminated feldspar ; a coarsely 

 feldspathic variety occurs north of Lenox, Mass. , and when it loses its 

 feldspar, it becomes cellular, like buhrstone ; at other places, as in 

 Cheshire, Savoy, and eastern Washington, Mass., the feldspar of a 

 feebly-consolidated quartzyte has been leached out by the filtrating 

 waters, and the rock reduced thereby to sand, excellent for glass-mak- 

 ing, while in some localities the feldspar so removed has been made 

 into valuable beds of white kaolin, as in Brandon, Vermont, East Shef- 

 field, Mass., and elsewhere. g. Gneissoid; containing some mica 

 and feldspar in layers, and so graduating toward gneiss, h. Andalu- 

 sitic ; containing andalusite, as in Mt. Kearsarge (Hitchcock), i. Tour- 

 malinic ; 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 Bennington, 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 the Southern New 

 Hampshire, in the Archaean area of Wisconsin, and in the Rocky 

 Mountain region, j. NovacuUtic-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, closeness 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 re- 

 ceived its impalpable 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 980, alumina 08, potash 06, soda 5, 

 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 

 coarser varieties are made into stones for bench tools. 



Beds of quartzyte have been made, like those of sandstone, out of the 

 quartz grains of older rocks, no evidence, chemical or geological, favor- 

 ing the view that they could be, or have been, produced by chemical 

 deposition. Some quartzytes and sandstones have had part of the 

 grains converted into more or less perfect quartz crystals, from the de- 

 position about them of silica in the process of consolidation — the little 

 heat required for making the siliceous waters coming from the earth's 

 interior, as a consequence of thick accumulations of strata above, or 

 from the friction of upturning, or from warm springs. 



2. Itacolumyte. — Schistose, consisting of quartz grains with 

 some hydrous mica ; on account of the mica in the lamina- 

 tion, it is sometimes flexible, and is called flexible sandstone. 



