KIMBERLITE FROM THE UNITED STATES 65
phyritic
' structure. A slice has been prepared for microscopic examination ;
but here, as in the case of the others mentioned below, a brief notice
will suffice, after Professor Lewis' elaborate description of the
Kimberley rock, for the general resemblance is very strong. In this
slice we find a number of grains, rather variable in size and form,
some approaching idiomorphic, others rounded or apparently broken, but
all serpentmised. Most of them were formerly olivine, but it is
possible that enstatite also may have been present. There are various
differences of detail in the colour and minuter structure of the
serpentine, in the distribution and arrangement of the iron oxide, and
the like; but on them it is needless to dwell. These larger grains are
scattered about in a more or less granular matrix, apparently identical
with that of the Kimberley rock, in which serpentine and a carbonate,
probably calcite with some dolomite, are important constituents. One
part of the slice suggests the presence of fragments of a peridotic
rock, embedded in a matrix of similar condition; but whether this is
significant of a pyroclastic structure or of a fluxion breccia is open
to question. Here, also, is a small ' patch ' of rather rounded mineral
fragments, which seem to be a felspar.
The rock from Kentucky is represented by the following specimens :—
(a) [435,
1.] ' Dyke I., Elliott Co. (Crandall).' A rock resembling that from
Syracuse in colour and aspect, but the fracture is a shade rougher, the
rounded spots run to a slightly larger size, being not seldom about
one-fifth of an inch in diameter ; they are less lustrous than in the
other case, and of a yellowish-green colour (similar to that in the
mottling of the other specimen and resembling that of olivine), and
thus lighter than the matrix. Except in this respect the two specimens
are very similar. Microscopic examination shows that this rock closely
resembles one of the best-preserved specimens from Kimberley. The
olivine
