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50 THE MATRIX OF THE DIAMOND
Kimberlite tuff occurs together with the Kimberlite breccia.
A
comparison of the Kimberlite with known ashes or tuffs, Professor
Rosenbusch having kindly placed his collection at my service for this
purpose, has failed to establish any analogy with them, and I am
compelled to differ from Professor Cohen and others who speak of it as
ash, mud, or conglomerate, and to regard it as a true eruptive lava.
The
structure of the African Kimberlite is equally shown in the Kimberlite
from Elliott County, Kentucky, and with that from Syracuse, New York. I
have compared the Kentucky rock with the African rock directly. Dr.
Williams has published a photograph of that from Syracuse.1
In mineral composition, in eruptive character, in structure, in
enclosures, the three rocks are identical. As the Kimberlite of
Kentucky and New York State occurs in dykes, not volcanic vents, it
becomes all the more certain that the porphyritic structure is an
original one characteristic of the rock.
Although,
as already stated, the peculiar character of Kimberlite is shared by no
other terrestrial rock, it is of high interest to find that in
structure it resembles meteorites of similar composition. Attention has
already been called to the likeness of some of its minerals to those in
meteorites, and its chemical composition has also been shown to be
closely related to that of the olivine meteorite called chassignite.
If
we were to replace the ground-mass of Kimberlite by native iron, we
should get a rock nearly allied in both structure and composition with
the well-known class of meteorites known under the name of chondrites.
These meteorites are both porphyritic and brecciated, and when the
breccia structure is well developed it has given rise to the same
• For notes upon specimens afterwards obtained from these localities by Professor Lewis, sec Section III,
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