B. K. Emerson—Diabase intersecting Zine Ore. 377 
rupted, and never more than six inches thick, runs nearly to 
the surface. This is the appearance of the dykes in the west 
wall. In the east, the dyke last cs eae is Ghickes and con- 
tinuous from top to bottom, and the two small dykes which start 
on the west from the foot of the main i are widely separated. 
The effect of these dykes upon the zinc ores is remarkable. 
Large portions of the eruptive rock have exactly the appearance 
of an amygdaloid, but the amygdules are spueres of green wil- 
lemite melted out of the vein, and such drops, together with 
franklinite could be found, though more oe in the coarsest 
rock, from the center of the main dyke naan one 
changed to a depth of a quarter of an inch or more into a red 
jaspery mass, which retains its thickness as the dyke thins, so 
that dykes less than an inch in thickness are made u who y 
of the brick red aphanitic material. In the thicker veins 
from which these filaments spring, the rock as a whole grows 
rock has the appearance of a very micaceous diorite; is brown- 
ish gray in the coarser varieties ~ nearly black in the finer, 
and varies from aphanitic to a coarser kind where the red mica 
is abundantly visible to the eye, ae more rarely small black 
augites appear. at is of high eet gravity and effervesces 
abundantly with acid. 
Th crostapicalli it resembles closely the finer grained, dark — 
colored elzolite rock from Beemersville which there seems to 
be an offshoot feo the great main dyke, and it was for this 
reason as well as to observe the effect of the large a 
of the zinc ellie investigated with the microsco The 
resemblance was not s sufficiently close to make it probable that 
the dykes of the two waar are of the same age and origin. 
Under the microscope the foreign constituents, franklinite, 
zincite, willemite and ia are present in large quantity ; 
the zincite easily mistaken for franklinite from its opacity but 
showing on the thinnest edges a deep blood red. The willemite 
is is especially abundant, both in round drops apparently melted, 
en, semi-transparent, fissured by many cracks, and show- 
ie feeble polarization,—and in broken — and large cleav- 
age pieces. It resembles sivite in many ways, having a 
out bright colors. In this respect it di ffers from the no weer 
willemite, which was sliced for comparison, from an inch ou 
side of one of the small dykes, which resembles and eke 
olivine in the brilliancy of its colors in polarized light. 
