276 Hanks on the occurrence of Durangite in Durango, Mexico, 
at three hundred. This gentleman thinks that the tin ore is 
still forming. He assures me that work having been sus- 
pended on a mine in 1864, a portion of the vein was left stand- 
ing. In 1870 he visited it again and found that new films or 
layers of cassiterite had formed, and in some places noticed 
that peculiar variety known as toad’s-eye tin which he believes 
had formed during his absence. 
These mines were discovered and worked on a small scale by 
the Spaniards from 1790 to 1824. From 1885 to 1846 they 
have been worked by Don Manuel Gracia, a native Mexican of 
Spanish descent, who amassed a fortune by extracting the tin 
and carrying it on mules to the city of Mexico, 590 miles 
distant. 
cafion, is nearly vertical, dipping but slightly. The fissure 1s 
filled with loose vein matter containing cassiterite in cylindric 
pieces, quite small. Crystals of durangite occur singly with 
cassiterite in the white pulverulent matter before described. 
Beautiful crystals of a larger size and of a light orange color 
are sometimes met with attached to the walls of the vem. 
have a few of these in my collection; they are quite different 
from those found in the vein matter. It was this variety which 
was first described by Prof. Brush. “+h 
he vein matter is described as being highly charged wit 
arsenic. When thrown into the furnace, so abundant are the 
arsenical fumes evolved that the workmen cannot endure rae 
and a preliminary washing process is resorted to, by which @ 
large proportion of the arsenical matter is removed. Some 
times in washing the vein matter, crystals of duane 
found, as are also those beautiful topaz crystals which ha of 
found their way to the cabinets of mineralogists in all parts 
the world. re 
I understand Mr. Boyd to say that the crystals of ce ns 
are only occasionally met with. The largest crystal know teat 
now in my possession. It weighs 3-022 grams. Its ore ik 
length is 19 millimeters and its extreme thickness pe 
meters. The edges are sharp and all the angles well of the 
and perfect. There aré some imperfections on some bling 
fac It is of a beautiful orange-red color, resem 
bichromate of potash. 1, and 
The crystals found in the vein matter are usually hem to 
of a darker color. On weighing one hundred of se only 
ascertain the average, I found their combined weight to 
7-750 grams. _- 
_ San Francisco, 619 Montgomery St. 
