'■^95J 549 [Crawford. 
Another stratum of arenaceous clay is exposed on the southern 
side of this ridge at an altitude of about 4,400 feet, near the 
crater in the cone Uval. A small stream of water percolates also 
from this bed of clay, but soon disappears through evaporation. 
Two other deposits of arenaceous clays were discovered on the 
southern side of the ridge at an altitude of about 2,000 feet, each 
interstratified with various kinds of semi-devitrified granopyric, 
pilotaxitic, and other kinds of lava. On the southern side of 
the ridge no sedimentary deposits were discovered in the fissures 
and ravines. There the volcanic extrusions were found to be 
basic in kind and increasing in percentage of iron and other 
metallic oxides toward the upper surface of the ridge. At a few 
places, however, near or at the floor of very deeply eroded 
ravines or at depths in fissures, the lava was composed principally 
of andesite, trachytes, and rhyolites. 
The foundation stratum on which Cerro Viejo stands is sand- 
stone interstratified with slate and magnesian limestone ; the 
latter containing masses of hematite and magnetite, weighmg 
from a few ounces to over a hundred pounds each, and cementing 
a large percentage of quartz sands. ^ 
More than a hundred large springs of water flow from the 
northeastern, southern, and northwestern base of the mountain. 
They are generally in groups, and range in temperature from 
70° to 100° C, many of them being of suflicient volume to form 
creeks from 20 to 40 feet wide and from 2 to 12 inches deep. 
Some of these springs have peculiarities worthy of special note, 
as the following descriptions of a few of them will show. 
Agua caliente del San Pedro, covering a depressed area of 
about 400 j^ards diameter, contains numerous springs of boiling 
or hot water. It is located at the northern base of the volcanic 
cone San Pedro, and has differently mineralized siibgroups, from 
some of which halcite crystalizes ; from another subgroup silicates 
are deposited, from another sulphides, and from another traver- 
tine. The water is too hot to permit excavations down to the 
1 This stratum of magnesian limestone and sandstone is exposed for about fifty 
miles at various places near the Pacific Ocean, commencing a few miles south of 
Cerro Viejo. It has been eroded deeply, leaving at many places on the surface of che 
magnesian limestone hundreds of tons of hematite mixed with quartz sands and 
hardened ; and for about 20 miles north of the Cerro it outcrops or is exposed by 
erosion at several places. It is of Paleozoic age, and on the south side of the Cerro is 
bisected for its entire length by a horizontal columnar dike about 12 feet wide. 
