30 CORUNDUM IN THE UNITED STATES. [bull. 180. 
The rock is fine "rained, of a rather light-gray color, and a decided 
basic appearance. Biotite is the most conspicuous mineral and occurs 
in small, flat, tabular plates, sometimes with distinct crystal outline, 
and up to a millimeter or two in diameter. In some specimens of the 
rock there are nodules, 5 to 10 mm. in diameter, that appear to be 
partially decomposed feldspar. The augite, which is prominent in 
the thin section, is not very apparent in the hand specimen. 
Prof. L. V. Pirsson, of Yale University, has kindly examined thin 
sections of this rock for me and says that the rock is an altered augite- 
mica-syenite. It contains unaltered phenocrysts of a clear brown 
biotite which are well crystallized and which sometimes show slight 
resorption. It also contains phenocrysts of augite of a pale-brown 
color, variable in size, the largest '2 mm. across, replaced in the majority 
of cases by pseudomorphs of calcite. Besides this pseudomorphous 
calcite there is also a considerable amount of this mineral in irregular 
masses or streaks, which may in part be the filling of steam pores and 
in part be pseudomorphous after hornblende; this, however, could not 
be definitely determined. The minerals just mentioned are embedded 
in a groundmass of a brown glass which is everywhere speckled and 
dotted with microlites of a lath-shaped plagioclase feldspar. These 
are small and somewhat altered, so that their determination is not 
entirely satisfactory, but they appear to be oligoclase. 
The rock is thus porphyritic, and the structure of the ground- 
mass is typical for the hyalopilitic structure of Rosenbusch. In many 
respects it closely resembles the augite-porphyrite of Weiselberg, 
weiselbergite. 1 
One feature that is brought out in the thin sections is the some- 
what laminated character of the rock in one direction, while in the 
slide cut at right angles to this a well-characterized flow structure is 
observed, all the longer axes of the minerals pointing in one direction. 
This indicates movements of flowing lava after the components had 
formed. 
The corundum crystals occur very sparingly in the rock, and those 
that were observed were not so sharp and distinct as the blue sap- 
phires. 
I could obtain no definite information regarding the location of 
Ruby Bar and no one of the bars is now called by that name. It is 
possible that the bar described by Kunz is the same as the one now 
known as French Bar. From the description given of Ruby Bar, it 
is apparently not so far up the river as French Bar. 
CORUNDUM IN SYENITE. 
On a high foothill between Gallatin and Madison rivers, in Gal- 
latin County, Mont., corundum has been found in a rock that is 
1 Rosenbusch, Mass. Gest., 3d ed., p. 953. 
