236 The American Geologist. April, 1892 
these it is, as usual, very irregularly disseminated. Some veins 
are altogether barren. In others is found a varying quantity of 
ore, never very large. Strings and threads and granules, often 
almost invisible, with occasionally a lump weighing a few ounces, 
or more rarely a few pounds, are the forms in which the cassiter- 
ite occurs. This, it may be remarked, is the usual mode else- 
where. In some instances, and probably either in choice speci- 
mens or in chosen localities, a yield of three and even of four 
per cent., has been reported. But a sanguine estimate for the 
productive veins of the region could not exceed two per cent., 
and even this could only be reached by careful work and the re- 
jection of poor material. The whole of the stanniferous material 
must be mined and picked over or crushed and washed in order to 
extract the ore,a process that entails considerable labor and expense. 
It would be premature to give any positive opinion regarding 
the contents of the veins as they are followed down, but judging 
from indications there is no ground to anticipate any change. 
The weathered material on the hill-side is scarcely richer than the 
lodes, nor are the ‘‘streamings”” to be compared in richness with 
those of some other parts of the world. Hence there is no rea- 
son to conclude that the portions of the veins already eroded were 
any richer than those now existing. Judging also from the ar- 
rangement and the structure of the veins they will run out down- 
ward as at the surface, and be succeeded by others, and they will 
a fact which 
certainly vary much in richness from place to place 
always renders lode-mining an uncertain occupation. 
There has been an immense expenditure of money during the past 
few years in the Hills,in mining machinery and other plant,and itis 
only reasonable to expect some return of metal from the outlay at 
no distant date. Enormous quantities of cassiterite undoubtedly ex- 
ist in the granite in spite of its sparse and fine diffusion in the rock, 
but the problem awaiting solution is whether or not it can be con- 
centrated and reduced at a figure that will afford a reasonable profit. 
[t is too early at present to say what can be done with better ma- 
chinery and methods, and the practice of the most rigid economy 
in the work. But the experience of a few years will show if the 
tin from the Black Hills can be produced at a figure sufficiently 
low to maintain itself in the open market of the world. If not, 
the subject of Dakota tin-mining will cease to be one of economic 
geology, and will become merely a question of the hight of the 
tariff-wall that can be built around it for its protection. 
