452 
of the loosened material, and the various me- 
chanical processes employed at the mines, and 
that pieces of such broken crystals would be 
separated and scattered to various parts of the 
immense dumping and weathering floors, never 
to be recognized as fragments of the same one 
when finally recovered, perhaps at very differ- 
ent times. 
The rock itself is a dark green, compact ma- 
terial, resembling serpentine and containing a 
large proportion of olivine, in grains and crys- 
tals; several green minerals that are not con- 
spicuous, from the resemblance of their color 
to the ground-mass (enstatite, chrome-diop- 
side, smaragdite and bastite); a mica, probably 
biotite, more conspicuous and quite abundant, 
and frequent grains of pyrope garnet, sometimes 
of gem quality and great beauty, and miscalled 
“Cape Rubies.’ Of smaller disseminated min- 
erals are to be noted perovskite, quite frequent, 
and magnetite, chromite, ilmenite and picotite, 
less so, though common. Rare and minute oc- 
currences are apatite, epidote, orthite, tremolite, 
tourmaline, rutile, sphene, leucoxene. As de- 
composition products there are serpentine and 
calcite, abundant, and zeolites, chaleedony and 
tale; also cyanite (?) These, with diamonds 
and included fragments of carbonaceous shale, 
make up the contents of this remarkable rock. 
Professor Lewis then goes into a detailed 
account of the mode of occurrence of these 
minerals, beginning with the most conspicuous 
species—the olivine—which is remarkable for 
its fine cleayage-surfaces and very interesting 
in its alterations. These are chiefly (1) into 
serpentine, proceeding from without inward, 
and penetrating along crevices and fractures, 
also sometimes in the form of chrysotile, pro- 
ducing a velvety border or coating to the grain; 
(2) tremolite, more internal, the fibrous struc- 
ture developing parallel to the vertical axis 
and domes of the olivine crystals; (3) when 
both these alterations are present and have 
gone so far as to obliterate most or all of the 
olivine, a talc-like substance intervenes be- 
tween them in which are developed minute 
needles of rutile, arranged parallel to the faces 
of the olivine erystal. The rock contains every 
stage of these changes from pure bright unal- 
tered olivine to those forms that have borders 
SCIENCE. 
LN. S. Vou. VI. No. 142. 
of serpentine or chrysotile, or incipient tremo- 
lite fibers within, to the complete alteration 
just described. The relation of all these to 
similar phenomena in other rocks, and in 
meteorites, is discussed with much fulness. 
Professor Lewis then takes up the smarag- 
dite, chrome-diopside, bastite and enstatite (or 
bronzite, for it is just on the line between the 
two varieties). The two first named are, in 
some cases, fine enough in color and clearness 
to yield gems, and also sometimes the bronzite ; 
all are colored by chromium. The diopside oc- 
casionally gives rise to calcite by alteration. 
The mica is next considered ; as all who are 
familiar with the rock are aware, it is the most 
prominent of the contained minerals to the eye. 
It is somewhat anomalous in character, being 
chemically a biotite, but optically nearer to 
phlogopite. It occurs in several distinct ways: 
(1) as included erystalline masses or plates, 
apparently an original ingredient of the rock; 
(2) surrounding grains of pyrope; (8) rarely, 
asa result of the alteration of enstatite; and 
(4) as a metamorphic product from the included 
fragments of shale; and the first form has pro- 
duced, by hydration, the vermiculite variety 
called vaalite, which occurs freely in the de- 
composed peridotite so largely known as the 
‘blue-ground.’ 
After referring to the pyrope garnets, and 
suggesting that the various garnetiferous ser- 
pentines are doubtless derived from the decom- 
position of similar peridotites, as further indi- 
cated by their likewise containing olivine, bron- 
zite, chrome-diopside, etc., he mentions another 
variety of garnets as found in this rock, very 
small, very brilliant, very hard, colorless or 
greenish, and extremely difficult to distinguish 
from small diamonds. These Professor Lewis 
is inclined to refer to demantoid. (?) 
An interesting part of this discussion next 
follows, in relation to the perovskite, which is 
pretty abundant in small crystals, of cubical 
habit. Professor Lewis gives much attention, 
and a number of drawings, to the optical fea- 
tures of this species, and strongly inclines to 
the view that regards perovskite as a highly 
twinned orthorhombic mineral and not isomet- 
ric save in external aspect. This has long been 
a mooted point, and these observations are an 
