i | 
1886.] Mineralogy and Petrography. 275 
micas, within which is a second belt of quartz and spodumene, 
Associated with the latter is the cassiterite in bunches, some weigh- 
ing as much as fifty or sixty pounds, Inside of this second belt 
is a third made up of greisen, in which occurs the granular va- 
riety of the ore. The central portion within the third belt is 
principally a coarse mixture of quartz and feldspar. The spodu- 
mene crystals in the second belt are of enormous size. One of 
the largest, measuring thirty-six feet in length, is without a single 
aw. The area of the tin-producing region is being constantly 
extended by new explorations, so that its limits cannot yet be 
definitely fixed. In addition to its occurrence in the rocks the 
mineral is also known to exist as “stream tin” in the water 
courses leading down from the hills into the surrounding plains, 
PETROGRAPHICAL News.—Feridotites—The rocks of this class 
belonging to the “Cortlandt series” on the Hudson river near Peeks- 
kill, N. Y., are divided by Dr. G. H. Williams! into hornblende 
peridotites (Hudsonites of Cohen), and augite peridotites (picrites 
of Tschermak). The former are characterized by the structure so 
well seen in the case of “ Bastite” or “Schillerspath,” and called by 
Pumpelly and Irving, “ luster-mottling.” In the present instance 
this structure (for which the author proposes the word fozcilitic) 
is due to the inclusion of olivine, or its alteration product ser- 
pentine, in hornblende. This hornblende is without crystal form 
and is filled with sharp little transparent crystals and opaque black 
needles. These latter occur also in the olivine and are identical 
with those which Judd? considers as of secondary origin. This — 
view the author of the present paper combats. He thinks they 
are substances extruded during crystallization as incapable o 
forming a part of their host, like the silicates in metamorphosed 
limestones, The hornblende peridotites pass, by the assumption 
of diallage, into the augite variety. Occasionally these become 
Schistose as the result of the action of great pressure. Color- 
ess augite with diallage-parting, hypersthene, brown horn- 
blende and well defined crystals of olivine are the most important 
Constituents of this rock. Variolitic granite—The first notice 
ba variolitic granite from Craftsbury, Vermont, appeared in Hitch- 
k's report on the geology of Vermont? The author there de- 
with considerable black mica. Scattered through this base occur 
P€arance. It occurs most abundantly just south of the latter ee 
mn, Recently it has been subjected to microscopical examina- se 
1 American our. Sci 
Ot. Jour. Pe - Science, v. XXXI, Jan., 1886, p. 26 
*Vol. 11, p. 564, 186r. 
, VOL. XX.—NO, u 
26. a 
Soc., v. XLI, Aug., 1885, p. 354- AMERICAN NATURALIST, Dec., 
