CHAPTER X. 



DESCRIPTIVE GEOLOGY OF NEW ALMADEN DISTRICT. 



[Atlas Sheets VII-XIII.] 



Character of the district. — The Ngw Almacleii, Enriquita, and Guadalupe 

 mines lie nearly south of San Jose, in a very attractive portion of the 

 country. The fertile valley of Santa Clara is in full view from many parts 

 of the region mapped, and the Santa Cruz Range, on the flanks of which 

 the deposits occur, is picturesque. Forests, gorges, and brooks diversify 

 the scenery, the character of which reminds one of portions of the Sierra 

 Nevada rather than of the Coast Ranges. This district has been much 

 more productive in quicksilver than any other in North America, and since 

 1850 it has yielded about four-flfths as much metal as the Almaden of Spain. 

 The general geology of the district presents one special feature of interest 

 in the occurrence of rhyolite, a lava not yet recognized at any other point 

 in the Coast Ranges. Otherwise the general geology presents no novelty. 

 The great opportunit}' which the district offers is for the study of structure 

 disclosed by the very extensive workings of the New Almaden mine, which 

 are said to measure 40 miles in length. 



Metamorphic rocks. — Tlio gvcater part of the surface is occupied ijy rocks 

 of the metamorphic series. The age of these rocks is known, for i\Ir. 

 Gabb found near the mines specimens of Aucclla. He does not, indeed, 

 describe the rock in which this characteristic shell was found, nor does he 

 give the exact locality, but from the various other occurrences mentioned 

 in this volume it is abundantly proved that the metamorphism was of later 

 date than the period at which Amelia flourished. The metamorphic rocks 



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