398 REACTION OF THE INTERIOR OF THE EARTH 



tinctly traced as " malpais," still devoid of vegetation, 

 and covered with scoriae and pumice, following a winding 

 course for distances of many miles, in the same manner 

 as around Hecla. About 70 geographical miles to the 

 west of the present Pueblo de Zuiii rises the lofty 

 volcanic mountain ridge of San Francisco itself, whose 

 summit is estimated at full 16,000 feet; it runs to the 

 south of the Rio Colorado Chiquito, and further to the 

 west follow Bill William Mountain, the Aztec Pass 

 (6279 feet), and the Aquarius Mountains (8526 feet). 

 The volcanic rock does not terminate at the confluence 

 of the Bill William Fork with the Great Colorado River, 

 near the village of the Mohave Indians (in 34JN. 

 114 W.); for several extinct, but stil] open, craters of 

 eruption can be recognised beyond the Rio Colorado, 

 near the Soda Lake. ( 545 ) Thus we see here, in the 

 present New Mexico, in the volcanic group of the Sierra 

 de San Francisco, to a little to the westward of the Rio 

 Colorado Grande or del Occidente (into which the Gila 

 falls), throughout an extent of 180 geographical miles, 

 a repetition of the ancient volcanic domain of Auvergne 

 and the Vivarais, and the opening of a new and wide 

 field to geological research. 



Also on the western side, but 540 geographical miles 

 more to the north, we find the third ancient volcanic 

 group of the Rocky Mountains, that of Fremont's Peak 

 and of the two " Three Mountains," which are very much 

 like the Trois Tetons and the Three Buttes ( 546 ), both in 

 conical form and in name : they are to the west of these, 

 and therefore further from the chain. They present 

 wide-spread and much rent and torn black banks of 

 lava, with a scoriaceous surface. ( 547 ) 



