164 J. P. Kimball on the Silver Mines of Sta. Eulalia, Mexico. 
Cretaceous fossiliferous limestone, with local lithological differ- 
ences, is the prevailing formation of the Rio Grande and Oon- 
chos basins, where, as seems likewise to be the case in Texas, 
within the development of the cantera it sustains throughout 
a metalliferous character. The mineral deposits of Sierra Rica, 
Cuchillo Parado, the Chupaderos, and the Chorreras in Chi- 
huahua are all contained in it. In the Santa Eulalia moun- 
tains is its most westerly development in any great prominence 
ane the valley plains, ee = seventy-five miles still furt 
est, a limestone is said to form the low base of the Sierra de 
Magistral, where it is feces metalliferous, and where, going 
as in other < Pagina el named, the cantera caps the higher eleva- 
tio ame is is applied in Northern aio to the bleached 
portion ore an Feoseritial alumino-siliceous rock, generally more 
or less econ | a 
oi variety of colors.* As elsewhere sieiation it is to the 
d precipi 
re, as elsewhere tous the sa Sra of the fossil 
iferous eee vom — npc have cu t bold, almost per 
within a couple of miles, omes the main formation, and 
rms the body of the range. No limestone ap in the 
de Dolores, seven miles to the north, where the San 
nh ae aa Toad crosses the Sta. Eulalia range; 
| mri the Sia, Wolalia it has already declined below the 
overlying cantera presents a greater developmen’ 
