ORIGIN IN IGNEOUS ROCKS. 47 
less and a strong, clear, brown tint. It occni-s in raised masses, i-arely showin*? 
crystal outline, and it contains a large anionnt of small apatite crystals. The 
pyroxene is of a pale-green tint, with the habit of diopside, and is tilled with 
many inclusions, now^ altered, but probably originally of glass; in some crystals 
these inclusions are so abundant as to rendei' the mineral cpiite spongy. The 
grains sometimes show crystal form, but are mostly anhedral and vary in size, 
though the evidence is not sufficient to show two distinct generations. 
These two minerals lie closely crowded together, and no feldspars are seen in 
the rock. The interstices between them consist of a small amount of a clouded, 
brownish, kaolin-like aggregate, which appears to represent some former feld- 
spathoid component, possibly leucite, perhaps analcite. * * * Some calcite 
in agglomerated granules is also seen in the section. 
This calcite does not appear to be of secondary origin, and is prol^a- 
bly due to fragments of limestone that Avere picked np as the igneous 
mass forced its way up through the limestones and were converted 
into calcite. 
In regard to the classification of this rock, Professor Pirsson" says: 
The rock appears to have its closest .affinities in the monchiquite group, of 
which it may be considered a basic, somewhat altered type. The abundance of 
biotite shows its relation to the minettes, but the rock is nnich richer in the 
lerromagnesian components and lacks the feldspar of the minettes. It has 
evidently a close affinity with the minettes and shonkinite of the region, and is 
clearly a more basic form of the same magma. It has the same richness in 
biotite and pyroxene as these, but differs in the feldspathic component. 
If Rosenbusch's classification is followed, this rock v>^oidd seem to 
be a basic member of the monchiquite-camptonite series of lampro- 
phyres, one end of which is characterized by an abundance of biotite 
and augite or hornblende. The rock is too rich in ferromagnesian 
and too poor in feldspathic constituents to be called a minette or 
kersantite, and the total absence of the feldspar and the small quan- 
tity of feldspathoid make it a very basic member of the general 
monchiquite group of Rosenbusch. 
The sapphire corimdum occurs rather sparingly in this rock in 
well-formed, tabular crystals of a blue color. They vary in size from 
very minute to half an inch in diameter and are of gem quality. 
The mineral does not occur in sufficient quantity to constitute a source 
of corundum for abrasive purposes, but it is of importance as a source 
of the sapphire gems. 
A kersantite described by Doctor Lossen, which cuts sedimoitary 
rocks of Lower Devonian age at Michaelstein, in the Harz Mountains, 
(xermany, and contains numerous inclusions, has also been found to 
carry corundum. This seems to be a closely parallel case to the one 
described above, except that the corundum occurs in such minute 
quantities as to be of only scientific interest. 
" Am. Jour. Sci., 4th ser., vol. 4, 1897, pp. 421-423 ; and Twentieth Ann. Kept. U. S. 
Geol. Survey, part H, 1900, pp. 552-558, 
