Review of Recent Geological Literature. 
203 
^submergence of the pre-existing land. This great quartzyte, which is un¬ 
doubtedly a part of the primordial, is apparently the equivalent of the 
“Red Sandrock” and the Granular Quartz of Vermont. It remains to be 
seen not only whether the lower quartzyte of the Black Hills may not be 
the equivalent of the top layers of the tilted quartzytes that carry the 
siliceous hematites there, as mentioned by Prof. Carpenter, and so be a 
part of his “slate series,” but whether they may not show as in southwest¬ 
ern Minnesota and in Vermont, a true primoidal fauna. This would 
further confirm their supposed equivalence with the primordial Taconian 
and would also indicate the propriety, even the necessity, of removing the 
whole “slate series” from the Archaean. 
Prof. Carpenter discards the idea that the granites of the Black Hills 
are of eruptive origin. “They seem to be true veins of the t} 7 pe known as 
-segregated veins—different from the true fissure veins in that they are 
parallel to the apparent bedding. Usually they are distinctly lens¬ 
shaped,” but some of them extend for thousands of feet. Their width 
varies from a few inches to over 100 feet. 
(2) Prof. Hofman’s report gives the details of the processes of treatment 
employed in the Black Hills with low-grade auriferous rock. All the 
mills, except the Caledonia, are constructed and operated practically on 
the same model—the Homestake—and are also under the management of 
the same superintendent. Including the Caledonia there are seven mills 
in operation, and they “drop 640 stamps.” After crushing, the ore is sub¬ 
jected, in the Homestake mills, to the battery amalgamation process. This 
begins in the mortar where mercury is added at intervals and continues 
till the amalgam reaches the apron plates w'here it is collected daily. A 
compromise is made between the two extreme methods of milling gold 
ore, that which mills large amounts and extracts carelessly as much gold 
as can be got in the hasty process, and that which extracts as much as 
possible at the expense of capacity. The amalgamation in these mills is 
carried on both outside and inside the battery. Within the small area of 
about 6,000 by 1,600 feet $2,271,341.14 were produced in 1887 from rock 
averaging $4.00 per ton in free gold. The report enters into the details 
of construction and operation of each of the mills, and describes the 
complement of men, accessories and products. 
In conclusion Prof. Hof man calls attention to the simplicity and effec¬ 
tiveness of the methods for extracting the free gold, and the waste that 
ensues in not extracting that which is involved with the sulphurets. This 
is allowed to disappear with the tailings, without any effort to secure it. 
He considers these tailings quite rich enough to repay working, as 3 per 
cent assays $24.00 per ton. In the not very distant future, as the free, 
gold becomes less and less in proportion to the sulphurets as the mines are 
worked deeper, the question of extracting the gold from the sulphurets will 
become one of practical and imperative importance. 
(3) Prof. Carpenter closes the report with a chapter on the character, 
occurrence and extent of the mineral resources of the Black Hills, treat¬ 
ing of gold, copper, nickel, tin, phosphates, and the various materials use¬ 
ful for construction. We believe this chapter contains the first systematic 
