iHqs.] 555 [Crauf.nd. 
only at a depth of over 100 feet beneath the tioor, excepting dur- 
ing the rainy season of each j^ear. 
2. Hojo de Sapote is near the southern base of the cone Viejo. 
It covers about twenty acres of land, and its floor is about 400 
feet below the surface of the earth at that part of the Cerro. An 
excavation to about 90 feet beneath its floor opened into a fissui-e 
from which carbonic oxide (CO.,) escaped. 
3. Hojo de los Canos, south of the base of the cone Santa 
Maria and near the eastern extremity of Corro Viejo, has a depth 
of about 300 feet, and includes an area of about twenty-five acres. 
Grasses and several varieties of trees flourish on its floor. 
4. In the same division of the Cerro there is another depressed 
area nearly as large and deep as Hojo de los Canos. 
The distinct inclination of the floors of these sunken areas 
beneath the Cerro is a feature worthy of note, and indicates that 
beneath the Cerro are large and deep caverns or grottoes that 
were excavated by hydrothermal and other igneous forces. 
The volcanic extrusions of which the Cerro is in large part com- 
posed appear to have been expelled during each time of volcanic 
activity in nearl}^ regular series as to texture of ejectamenta, and 
the series appear to have followed each other in order of composi- 
tion usually from the more acid to the more basic. So far as 
observations on the surface and in deep ravines in the ridges and 
cones indicate, the extrusions in the Cerro from its base level 
[i. e., the present stirface of the valley from which it rises) up to 
about one half its height are composed of rhyolites, trachytes, 
phonolites, pumice, and other acid lavas in greatest proportion. 
In cooling, these have assumed vai-ious textures, as hyaline and 
scoriaceous-crystalline, and are intermixed with trachy-dolerites, 
hardened-amorphous silicates, Infusoriae, and fragments of syen- 
itic and granitic igneous rocks. The cones and .upper parts of 
the ridges are composed largely of hardened aphanitic and hya- 
line lavas and ejectamenta of peperino, while masses and fragments 
of dolerite, basalts, and other basic rocks are exposed in large 
(}uantities at their ba^es, and also form a small ridge near the 
foot of the Cerro whither they have been sent by the jarring of 
earthquakes and volcanic disturbances or have been transported 
in floods of mud (aluvions del barro) dtn-ing heavv and long con- 
