252 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1902. [bull. 213. 
Sabanilla Railway crosses the same range in a deep notch or pass. 
On both sides of the railroad south of this pass there are several old 
manganese mines in rocks belonging to the upper part of the mixed 
volcanic and marine series. The manganese was also formerly 
worked near the station of Dos Bocas, several miles west of the 
deposits located south of Cristo, and apparently in rocks occupying 
approximately the same stratigraphic position. The beds exposed in 
these mines are very much disintegrated, and the rock is frequently 
impregnated to a considerable extent by manganese ore. It is varie- 
gated in its coloring, being green with red splotches. It exhibits no 
gritty material, and it appears to have been made up of fragments 
which were originally angular in form. At the Boston mines, located 
between 2 and 3 miles to the east of Cristo, the country rocks are 
limestones and glauconitic greensands, cemented by lime, and both 
of these rocks are found replaced by ore. When decomposed they 
resemble the disintegrated beds south of Cristo. 
In the deposits south of the Cristo divide, between the drainage 
which flows directly to the sea by way of Rio San Juan and the basin 
of the Rio Cauto, which finds its outlet to the west of Cabo Cruz, the 
strata all dip at varying angles toward the north, excepting in such 
instances as they are overturned, when the reversed dips are very 
steep toward the south. Associated with the ore there are large 
amounts of siliceous rock in the form of dense amorphous jasper, or 
bayate, as it is locally called. Traced in a broad way, the bayate 
may be made out to follow the stratification of the bedded rocks, 
along which it occurs in interrupted masses. But studied locally, the 
irregularity of the bayate is such that, with the poor exposures of 
the strata which exist, it would be impossible to say that it did not 
have the form of cross-cutting veins, as sometimes appear. However, 
the interbedded character of the siliceous rock is established with a 
good degree of certainty. Across the stratification the thickness of 
the jasper masses is found to vary from a few inches to 15 or 20 feet, 
while along the bedding they may have a length reaching in some 
cases several hundred feet. 
The ore occurs principally in a very irregular way, filling spaces 
between the jasper and the country rock, but also in the form of veins 
in the masses of jasper, and disseminated through the decomj)osed 
country rock adjacent to the jasper. In the last case the ore frequently 
has the form of nodules arranged in the bedding planes of the parent 
rock, which it seems to have replaced in part. The relations of the 
ore and the jasper are very intimate, and specimens may be found 
in which veinlets of ore penetrate the jasper as though there had 
been molecular replacement of the latter by the former. On the other 
hand, cases may be observed in which the opposite condition seems 
to have obtained, so that the ore w r as replaced by siliceous material 
introduced after the first deposition of the metallic mineral. In gen- 
