34 BULLETIN 61, U. S. DEPAKTMENT OF AGBICULTURE. 
area of the sink; the second, on the outside margin. In the first boring borax is 
shown in percentages ranging from 1 to 5.5, and at depths extending from 18 to 50 
feet. Below this depth traces of borax occur, while in the material extending from 
the surface to 18 feet practically no borax, or only a trace, was found. In the second, 
borax was reported in percentages ranging from 5.56 to 6.57 and extending from a 
depth of 30 to 45 feet. Above and below these depths only traces of borax were 
reported. The results of these borings would indicate that in some of the playas, at 
least, might be expected concentration of borax minerals at depth. 
The minerals reported from deposits of the playa type are borax (sodium borate), 
ulexite (sodium calcium borate), and colemanite (calcium borate). The content of 
the crude material ranges from 5 to 20 per cent boric acid. Deposits of this type 
are no longer of economic importance. 
Deposits of the second type are the important sources of borate minerals. In the 
basin region they are worked at Ryan and in the vicinity of Furnace Creek (Mount 
Blanco). For a description of these deposits the reader is referred to Campbell 1 
and to Keyes. 2 
These deposits are of importance in that they account for the source of a part, and 
perhaps the principal part, of the borate material in certain playa deposits, notably 
those in Death Valley and along the Amargosa Paver. Of the bedded deposits Keyes 
describes two general types. The one is illustrated by the mines northwest of Dag- 
get, Cal. In this locality the borate minerals are found in a finely divided state in 
beds of blue clay. The workable beds contain from 10 to 12 per cent boric acid. 
The other type is characterized by nodules and masses of almost pure colemanite in 
clays and shales of Tertiary age. Respecting the origin of these deposits, Charles 
Laurence Baker, 3 after discussing the possible formation of the deposits by the evapo- 
ration of a body of water of considerable depth, presents the following: 
"The alternative hypothesis that these minerals had their immediate origin in hot 
springs and solfataras opening directly into shallow lakes, perhaps only of seasonal 
duration, or in playas, has much to commend it, especially when considered in 
connection with the numerous evidences of shallow water deposition. These evi- 
dences comprise ripple marks, sun cracks, and rain prints, which are found on the 
finer as well as the coarser beds, and the layers of finer breccia and conglomerates 
interbedded with the fine shales and tuffs. Shallow lakes or ponds probably existed 
at times during the deposition of the fossiliferous tuff member, for tbey seem to be 
necessary to account for the presence of the gasteropods. The paucity or absence of 
fossils in the borate and the fine ashy and shaly tuff members, as well as the presence 
of the colemanite, limestone, and gypsum layers, apparently indicates the salinity 
of the waters. 
"There was great volcanic activity before and during the deposition of the Rosa- 
mond. The larger fragments of lava were most probably derived from flows subject 
to erosion somewhere in the area tributary to the basin of deposition. Interbedded 
flows of both acidic and basic lavas make up a part of the Rosamond. But the fine 
volcanic ash was probably blown in by the wind or settled during explosive volcanic 
outbursts and need not have come from the immediate vicinity. The common view 
of the origin of calcium borate from solfataras and hot springs associated with the 
abundant contemporaneous vulcanism is likely to prove to be the correct explanation 
for the borax beds in this region. " 
I am in accord with the main points in Baker's view. It must be noted, however, 
that in the colemanite deposits of the type exemplified by Mount Blanco a consider- 
able amount of secondary action is noticeable. There are many distinct veins of 
colemanite associated with the layer beds. One gets the impression that these are any- 
thing but bedded deposits. I am inclined to the view that the Mount Blanco deposits 
represent the solution of the borate minerals from beds and their concentration in more 
or less open fissures in close proximity as veins. 
ALUM. 
Spurr 4 reports a deposit of alum and sulphur 10 miles north of Silver Peak, Nev. 
The area in which this mineral occurs is about 200 feet in diameter. The alum is asso- 
ciated with sulphur in rhyolite. It forms a network of small veins in the broken 
rhyolite. The rhyolite is intrusive in Tertiary sedimentaries. The mineral is a pure 
potash alum, kalinite. < Spurr considers that the alum results from the action of 
steam and sulphuric acid emitted from solfataras. The acid attacks the potash and 
alumina of the rhyolite and forms kalinite. 
i Bui. No. 200, U. S. Geol. Survey. 
2 Borax deposits of the U. S., Trans. Am. Inst. Min. Eng., vol. 40, p. 674. 
3 Bulletin of the Dept. of Geology, Univ. of Cal., 6, p. 358. 
* Professional Paper No. 55, U. S. Geol. Survey, p. 157. 
