E. & Dana—Association of crystals of Quartz and Calcite. 449 
The specimen in hand was obtained by the writer in August, 
1875, when visiting the Yellowstone National Park in connec- 
tion with the party of Col. William Ludlow, U.S. A. It was 
found in the neighborhood of what has been called ‘‘ Specimen 
Mountain,” a locality which has furnished many fine amethysts, 
geodes of chalcedony, and fragments of silicified wood. The 
rock is an igneous conglomerate. : 
The specimen itself consists mostly of chalcedony, upon the 
surface of which have been implanted rhombohedrons (— }/) of 
calcite, and finally, as a still later process, the quartz has 
incrusted both the calcite crystals and simultaneously the ex- 
posed surfaces of the chalcedony. In the latter position a 
simple drusy surface of fine quartz crystals, irregularly planted, 
has resulted, but the crystals upon the calcite, though unques- 
tionably of simultaneous formation, are all in a similar parallel 
position, analogous to that shown in fig. 1; the pyramidal faces o 
the quartz crystals (22 or —#) being parallel to the rhombohedral 
(-R) face of the underlying calcite. In some cases a collection 
of small parallel crystals of quartz form a coating upon each 
crystals is very uniform ; itisshown 
In fig. 2. the smaller crystals 
(to finch broad), the symmetry 
of the planes was nearly as perfect 
as in the drawing. A comparison 
of this figure with those given by 
vom Rath will show that though in 
the Sepa features similar, still the — ae tebe 
one here given differs in some most 1mpor . 
The first examination of the ov gaggeste t° apes 
x} ‘ee bn : Ee y thy ] ? 
rn of the zon (3) pt” aye ve ct 
1 around the erystal are obviously repetitions 
of the same series of plan A more critical re Ao aon 
however, by the aid of the reflecting igoapeeaige he oles 
Sy a eee Sk vpavaltel iba is very slight. 
tr 
they are continued aroun 
time that the deviation from pe 
It is in fact a remarkable case of pseudo-symmetry- 
