214 TRANSACTIONS OF THE [Apr. 24 
In the white and gray varieties of the rock, a small quantity 
of argillaceous material coats the sand grains. The presence 
of this thin coating, particularly when it is hematite, gives to 
the outlines of the grains a clearness that they would otherwise 
lack. When, as is sometimes the case, the coating is absent it 
becomes difficult to draw any line between the grain and the 
surrounding cement. 
The rock affords an excellent example of the secondary 
enlargement of quartz grains described by Sorby, * Irving 
and others. About every sand grain quartz has been deposi- 
ted until further growth was checked by contact with the 
quartz forming about adjacent grains. This secondary quartz 
always shows perfect optical continuity with the original quartz 
of the grain about which it is deposited. As arule there is no 
opportunity for the development of crystal outlines, the process 
being too complete, but one or two faces are occasionally 
formed. 
As a result of this process the rock is thoroughly indurated, 
being practically a solid mass of quartz. 
PYROXENE ROCKS. 
Near the base of the crystalline limestone, and seemingly 
interstratified with it, is a body of schistose, highly contorted 
rocks of somewhat doubtful character. In the field they were 
taken for metamorphosed sediments, and no particular attention 
was paid tothem. But a microscopic study reveals a mineralogi- 
cal composition that suggests the possibility of an igneous 
origin. Against such a supposition, however, strong evidence 
is afforded by the gradual transition often seen from limestone 
to pyroxene rock. While there is considerable diversity in the 
composition of different portions of these rocks, one variety 
is particularly abundant. It consists of feldspar, quartz, 
monoclinic pyroxene, mica, titanite, apatite, graphite, pyrrhotite, 
and pyrite. 
Both orthoclase and plagioclase are present, sometimes one, 
sometimes the other predominating. In some sections they are 
very fresh, in others completely altered to muscovite and kaolin. 
Quartz is usually in small quantity or lacking. In a single 
section, where it is uncommonly abundant, it shows a serpen- 
tinous alteration along cracks, similar to that described and 
* Sorby, H. C., Proc. Geol. Soe. Lond., 1880, p. 62. 
t Irving, R. D., Am. Jour. Science. III., XXV., p. 401. Bulletin 8, U.S. G.S., 
5th Ann. Rep., U.8. G. S., p. 218. 
