Hidden and Washington— Contributions to Mineralogy. 508 
were covered with beautifully crystallized muscovite, quartz, 
dolomite, siderite, apatite and rutile. All the contents of this 
large pocket had a thin chloritic coating, which could easily be 
removed, in most instances as a very friable shell. The rutile 
exhibited twinning according to both the known laws, and 
often both were to be noticed in the same crystal. Crystals 
with geniculated members of from 1 to 2°" long and 5™™ thick 
were not uncommon, and a few simple crystals were 6 in 
length and 1™ in thickness. All were terminated with well pol- 
ished planes, s(111) and e(101) being dominant. The dolomite 
as also the siderite crystals showed only the unit rhombohedron 
and basal pinacoid. These planes were very flat and well pol- 
ished, no curvature of the planes, as is peculiar to the species, 
being observed. The rhombohedral face was striated horizon- 
tally. Twins of dolomite were common and calcite crystals 
were observed in parallel position on the rhombohedral face 
in several instances. One of the dolomites measured nearly 
10™ on its edges and was a very exceptional example of the 
species. In this pocket were found a few apatite crystals of 
unusual perfection, and these we notice in detail. 
APATITE.—It was plainly evident from their loose attach- 
ment and perfection of form that these crystals were the last 
erystallization of the pocket. For the most part they were 
rather long, slender prisms, 15 to 25™™ by 2 to4™™, of a pale 
bluish green color and transparent. A sort of parting parallel 
to the base was quite noticeable, and the terminations were often 
highly modified, though, as a rule, only with the more common 
planes. In one corner of the pocket a small group of musco- 
vite crystals was found which had implanted on them a few 
very brilliant, wine yellow, transparent, lenticular crystals of 
apatite. They were of an entirely different habit from the rest 
of the apatite found, and one of these we have selected for 
measurement and description. The particular crystal examined 
was quite small, about 2" in diameter, and, with the exception 
of part of one side, where it was attached to the mica by the 
prism, was almost perfectly developed both above and below. 
Its habit is almost unique, Schrauf* only figuring one crystal 
fig. 23, xx) at all similar. The-pyramids r (1012, 4), x (1011, 1), 
and s (1121, 2-2) predominated, while the prisms were nearly 
absent. Another interesting fact in regard to this crystal is 
the occurrence of both hemihedral prisms h (2130) and h, (1230). 
The planes observed were as follows: 
Basal pinacoid, ¢ (0001, O), prisms, 7m (1010, 7), a (1120, 7-2), 
A (2130, 2-8), h,(1230), pyramids, 7 (1012, 4), x (1011), y (2021, 2), 
z(8031, 3), v(1122, 1-2), s(1121, 2-2), dihexagonal pyramids, 
v (2131, 3-2), 7(2132, 3-2) and 0(8142, 2-4). 
* Atlas der Krystallformen, Plates xviii to xx. 
