376 = BB. K. Eimerson—Diabase intersecting Zine Ore. 
So =o Yo 
Bet, +5 
hence we obtain 
Me Lams Fi -¢ 
of eas : —! i rg a 
a prea the zenith distance of the pointing by z we 
should hav 
(C2 + Yo) Sin 2 = ee +9. = F 
(cx, + ¥o) i 2=cr'+y'=F", 
etc. 
provided the law, that ie tees varies as the cosine of the 
altitude, is correc 
If the measured values F, F’, ete., are not satisfied by the 
above equations, the wea will furnish data for obtaining 
the form of the function which, when substituted in the place 
= sin z, will best represent the observed readings. Any 
en apparent change in the flexure, as for instance the shift- 
ing of the object-glass in its cell, could be observed directly 
by keeping the eye at the instrument while it is being revolved. 
In some cases it might be well to fasten the mirror “to the cell 
instead of to the objective. Thies the flexure has been deter- 
mined, a thin strip of metal, the weight of which is exactly 
equal to the weight of the mirror, can be wound around the 
object end of the tube. 
Art. XLL—On the dykes of Micaceous Diabase penetrating the 
bed of Zinc Ore at Franklin Furnace, Sussex County, New 
Jersey ; by Ben. K. Emerson. 
. reat open working at the Taylor mine in the “ Buck- 
heat ield,” at Franklin Furnace, is carried forward for a Jong 
distance with a width of perhaps fifty feet and a depth of ninety 
feet. As the limestone bed dips 90°, the walls are os and 
as the ore body in this limestone bed has a steep pitc oY 
north, the mine is at its north ona no longer wo 28g ou 
day, and as if planned specially for the convenience . she 
ee: a preety ss ar 20-22 feet in width cuts the lime- 
and the ore bed at this point, and standing vertically 
shes at right ‘Mgles across the mine like the partition wall 
of a burned building. Seventy feet above the floor of the 
mine sn again at the bottom passages have been cut through 
the dyke to get at the ore behind. From a point near 
dipping 50° S., widenin ng and narrowing and sending off emall 
branches. These smaller dykes do not exceed two feet in 
thickness. T'wenty feet farther south another dyke more inter- 
