CORUNDUM IN IGNEOUS ROCKS. 45 
bro\Yn 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 pseudo- 
morphons 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 men- 
tioned are embedded in a groundmass of a brown glass which is 
everywdiere 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 groundmass 
is typical of the hyalopilitic structure of Kosenbusch. In many 
respects it closely resembles the augite-porphyrite of Weiselberg, 
weiselbergite.'^ 
One feature that is brought out in the thin sections is the somewhat 
laminated character of the rock in one direction, while in the slide 
cut at right angles a well-characterized flow structure is observed, all 
the longer axes of the minerals pointing in the same 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 found in the gravels. 
No definite information regarding the location of Ruby Bar could 
be obtained, and no one of the bars is now called by that name. It is 
possible that the bar described by Mr. Kunz is the same as the one 
now known as French Bar, though from the description given of 
Ruby Bar, it is apparently not so far up the river as French Bar. 
Corundum in andesite has also been descril^ed from several Euro- 
pean localities. Osann ^' found corundum associated with spinel, bio- 
tite, sillimanite, andalusite, rutile, zircon, etc., in a mica-pyroxene- 
andesite in the vicinity of Cape de Gata, in southeastern Spain. The 
corundum forms flat, basal plates Avith striations parallel to the 
rhombohedron. The rock also contains numerous dark micaceous 
inclusions. 
Dr. A. Lacroix^ describes the occurrence of corundum in the 
trachytes, andesites, and basalts of the volcanic district of the 
Auvergne Mountains in the central plateau of France. The corun- 
dum is associated with zircon, diaspore, sillimanite, etc. The rocks 
also contain numerous acid inclusions that have been more or less 
« Kosenbusch, Massige Gesteine, Sd ed., 1896, p. 953. 
" Zeitschr. Dcutschen geol. Gesell., Berlin, vol. 41, 1889, p. 297 ; vol. 4:}, 1891, p. 688, 
<^ Bull. Soc. mineral. France, vol. I'A, 1890, pp. 100-106, etc. 
