868 J. D. Dana on the Quartzite, Iimestone, ete., 
C. Quartzite beds.—The rocks of the quartzite beds differ 
much in character. The principal kinds are the following. — 
(1.) An intensely hard, gray or whitish quartzite, jointed 
profoundly and in more than one direction, but without distinct 
traces of bedding. me beds are a conglomerate of the same 
hardness, made up of pebbles or stones from the size of a pea 
to that of cobble stones. Minute particles of pyrites are spar- 
ingly disseminated through a large part of this and other 
varieties of the quartzite. _ 
(2.) A rock equally massive in fracture and almost as firm, 
but showing the bedding more or less distinctly. (It is often 
used for the hearths of furnaces.) Cleavable particles of a 
glassy feldspar are sometimes distributed through it. When 
thus laminated it often contains, especially over the surfaces of 
the lamine, scales of a white mica or hydro-mica, and sometimes 
minute brown or blackish tourmalines. 
A rock of this kind often weathers rapidly on exposure, SO 
as to become very friable, or even fall to sand. (It is used for 
making glass in the region.) 
: (3.) Soft sand-beds, in thin layers, that change deeply to 4 
irty sand. ‘ 
(i) Caleareous quartzite, which graduates on one side wees 
limestone and the other into quartzite. Some hard laminat 
quartzites are very porous as if they had once contained calea- 
reous material. : 
(5.) Gneissic quartzite and quartz-conglomerate. A variety 
consisting partly of quartz pebbles half an inch to an inch m 
diameter containing large masses of orthoclase and much mica 
and really a variety of gneiss. 
(6.) Feldspathie quartzite, a quartzite, often very hard, con 
taining much orthoclase through its mass. The orthoelat 
ecomposes easily and becomes removed, leaving the rec 
cavernous, and thus, as Hitchcock long since explained, 18 pt 
duced the buhrstone of Berkshire. Besides the orthoclase, a 
glassy cleavable less alterable feldspar may often be oor 
guished in the so-called buhrstone, and sometimes in the wa 
of the cavities that had been made by the decomposition an 
removal of the orthoclase; it is probably either albite oF 
oligoclase.* sarees 
The transitions between the different kinds of rock in thé 
quartzite formation are often very t. Only a few 
sometimes separate the regularly-bedded fragile quartzite from 
the hard bedless granular quartz. The soft sand-rock pape 
has within it intensely hard masses made up of the sands © 
__ *I am indebted for specimens of this and the preceding variety of the quartz 
‘Brook and Mill Biver, east of New Lenox. n=? we "0m fe valeve-l 
