ON ITS EXTERIOR. VOLCANOES. 397 



River to Santa Fe del Nuevo Mexico, there are two 

 extinct volcanoes, the Eaton Mountains ( 543 ), with 

 Fisher's Peak, and (between Gralisteo and Pena Blanca) 

 the hill of El Cerrito. The lavas of the first of these 

 cover over the whole country between the Upper Arkan- 

 sas and the Canadian River. The peperino and volcanic 

 scoriae, which begin already to be found in the prairies 

 in approaching the Rocky Mountains from the eastward, 

 may perhaps belong to ancient eruptions of the Cerrito, 

 or possibly even of the great Spanish peaks (37 32' N.). 

 This eastern volcanic domain of the isolated Raton 

 Mountains forms an area of 80 geographical miles in 

 diameter ; its centre is somewhere about 36 50' N. 



On the western slope of the Rocky Mountains, the 

 most clearly marked evidences of ancient volcanic ac- 

 tivity occupy a much wider space, which has been 

 traversed throughout its breadth from east to west by 

 the important expedition of Lieutenant Whipple. 

 This area, which is exceedingly irregular in outline, and 

 is moreover interrupted for a length of fully 120 geo- 

 graphical miles by the Sierra de Mogoyon, is comprised 

 (always speaking according to Marcou's geological map) 

 between the parallels of 33 48' and 35 40'. These 

 outbursts have therefore been more to the south than 

 those of the Raton Mountains : their mean latitude is 

 nearly that of Albuquerque. The area thus spoken of 

 divides itself into two sections ; that of the part of the 

 crest of the Rocky Mountains near Mount Taylor, 

 which terminates in the Sierra de Zuni ( 544 ), and the 

 more western division, called Sierra de San Francisco. 

 The conical Mount Taylor, 12,256 feet high, is sur- 

 rounded by radiating lava-streams, which can be dis- i 



