Geological and Typographical Features — Wittmann 173 
by an isolated mountain, some four miles long and two and 
a half wide called the Sierra del Topo, renowned for its 
hot sulphur springs which appear on the southeasterly 
slope near the little village of San Bernahe. 
Farther north are other mountain ranges which close 
the valley on three sides, having their slope from west to 
east, with the Sierra del Topo as a center. 
On the east side are low hills, between which the riv- 
ers Santa Catarina and Pescaria find their way. 
Such is the topography of Monterey as it appears to- 
day. But what enormous changes must have taken place 
in former periods! 
The Sierra del Topo and the Topo Chico which rise 
out of the plain that bounds the city on the north, are of 
plutonic origin, overlain by vast diluvial formations, to 
which class all the other ranges also belong. 
The Topo Chico is of a nearly pure limestone (99.20%), 
very glossy, but semi-cristalline, witli veins of pure gypsum 
and numerous '"blow-outs" (galena) near the summit, with 
lead deposits at its northwesterly foot, and sulphur springs 
of a temperature of 102' Fahr. on the east. The strata of 
the surrounding mountains indicate an upheaval towards 
the Topo Chico. They consist also of limestone of varying 
density, intermingled with magnesite, etc. 
Imbedded in these mountains are large deposits of iron 
and lead ore. mostly in pockets, as well as deposits of rock 
salt and other alcaline rocks with sulphate of soda in excess. 
In many places the soluble portions of these rocks are 
washed out, leaving channels for the subterranean water- 
courses, some of which are sweet and others more or less 
mineralized. 
At a former period, probably after the upheaval of the 
Topo Chico mountain, the valley of Monterey was a vast 
lake. The foremost scientist of his day, Alexander von 
Humboldt recognized this fact. Natural appearances indi- 
cate that the present level of Monterey was probably more 
than 160 feet below the surface of this lake which must 
have been inclosed by hills on the east side of the valley, 
through which at a later period it found an outlet. The 
evaporation from this lake must have been enormous, and 
