spencer.] MANGANESE DEPOSITS OE SANTIAGO, CUBA. 253 
eral the mode of occurrence is such that both the ore and the associ- 
ated jasper appear to have been introduced in a secondary way after 
the deposition of the strata in which they are found and the original 
substance of which they now replace. The jasper and the oxides of 
manganese are of contemporaneous origin, and for their introduction 
into the strata where they now occur the action of the heated water 
in circulation is suggested. The constitution of the greensand beds 
was evidently favorable for a chemical reaction between their substance 
and the materials held in solution by ascending hot waters, which 
doubtless, originating at a considerable depth, found easy channels 
of outlet through the more porous of the disturbed and upturned 
strata occurring in the region. 
Oilier manganese mines, and in fact the only ones at present in 
operation, lie about 3 miles east of Cristo, and 12 miles to the north- 
east of the same town. The former comprise the Boston group of 
claims already mentioned and the Ysabellita near by, and the latter 
includes the Ponupo mines. Owing to the limited time at the writer's 
disposal it was impossible to sufficiently test the theory formed in the 
field that all of these deposits lie at approximately the same geo- 
logic horizon. There are, however, some facts which tend to sup- 
port this idea. Perhaps the most important of these is the occurrence 
of a band of limestone, composed almost entirely of foraminifera 
belonging to the type Oi'bitoides, just above the ore horizon at four 
distinct and widely separated localities, namely, near the mines cast 
of the railroad south of Cristo, at the Boston mines, at the Ponupo 
mines, and at San Nicolas, about 8 miles west of San Luis, where 
manganese ores also occur in green, disintegrated sandstones. Again, 
in almost all of the places where the strata in which the ores occur 
are exposed, they are exactly similar, being loose, disintegrated sand- 
stones, mostly of a dark green color. At the Boston mines the green, 
decomposed sandstones have been uncovered at a short distance from 
the ore body, and here, though resembling in general appearance the 
sand which occurs with much of the ore, they are found to be made 
up in large part of the shells of a large variety of foraminifera filled 
with glauconite and accompanied by grains of the same mineral to 
which the green color of the sandstone is due. It seemed evident that 
these rocks and the ore-bearing beds were originally of the same 
nature, but that the calcareous shells of the foraminifera had been 
removed from the near neighborhood of the ore deposits by the solu- 
tions which deposited the silica and manganese. A similar removal 
of the calcareous contents may be taken to explain their absence from 
the other localities, where the only strata observed were those in 
close proximity to the ore bodies and jasper. 
The rocks in the region south of Cristo were found to have been 
tilted toward the liQrth, as though they were lying upon the south side 
of a great structural syncline. This, in fact, they do, as more gen- 
