B. K. Emerson— Diabase intersecting Zine Ore. 379 
in the main dyke showed under the curtains a uniform gray 
ground difficult of resolution and resembling that of a phono- 
- and reguiarly mottled by abundant mull rounded opaque 
ots. 
Whe en examined with a power of 600, it is found to show 
small portions of a colorless isotropic glass which is crowded 
with minute particles apparently spherical scattered either 
singly or joined three or more together into moniliform rods, 
or, finally, densely agglomerated into the opaque spheres with 
which the ground is mottled. These products of the devitrifi- 
cation of the glass-base bear close resemblance respectively to 
the eichicn margarites and cumulites of Vogelsang, except 
that — do cert ainly polarize li an 
s background appear (a) nee ne well-formed crys- 
tals a franklinite or magnetite, (b) very abu evi clear hex- 
agonal cross-sections which appear to sca tite, and others 
larger and clouded with the included mieroits whieh m may be 
nephelite, (c) small very regular sections of p i 
sometimes beautifully — and (d) rare sales and needles 
fibrolite, bys extinguish the light at an angle of 37° with the 
vertical axi 
he een erystalline constituents described are here scat- 
tered ata distance from each other in the a ground 
mass and show a very distinct fluidal struct 
Finally, in the jasper-like material of the narrow red _fila- 
ments, the ground is in thin section deep red and the mate- 
rial resembles the basic volcanic glasses in the difficulty of 
getting a transparent slide. e ground has however under- 
gone complete or almost com plete devitrification and the 
opacity is caused by the close aggregation of minute grains 
resembling those of the preceding variety but redder and even 
more minute than they, which gave when the light could be 
driven through the thinnest portion of the slide bright aggre- 
gate polariza 
Quite large, pieces of included willemite and zincite occur 
abundantly. The zincite is of so deep color that by ordinary 
light most of the pieces are quite opaque and only here an 
there a blood red light penetrates a small portion of the sur- 
face. Curiously with erossed Nicols these masses of zincite 
glow out like carbuncles and the bright red of the background 
quite pales beside it. It is at the same time quite apolar. 
A multitude of sharp hexagonal apatite cross-sections let 
the light through the dark ground, and the same pale brown 
augite and red mica appear as in the other yarieties, 
