266 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



arate this portion from the valley through which the Rio 

 Grande runs, after making its turn southward, west of Fort 

 Garland. This region, geologically, is more interesting than 

 the western one, on account of the evidence furnished dem- 

 onstrating the existence of two very large lakes at the close 

 of the volcanic activity there. The two were connected by 

 a narrow strip of water south of Fort Garland, and the lower 

 one extended southward nearly to the Rio Colorado. At 

 that time, too, the course of the Rio Grande was different 

 from its present one. By the formation of a narrow canon 

 in the basaltic beds, the course of the river was deflected, 

 the lakes drained, and the topography left very nearly in 

 the shape we now observe it. The accurate determination 

 of all the points connected with the existence of these lakes 

 offers no material obstacle, but requires far more time than 

 could be bestowed upon it in the regular course of the sur- 

 vey. 



Separating the eastern foot-hills and the great plains from 

 the San Luis Valley is the southern continuation of the San- 

 gre de Christo Range. Several peaks of this range rise to 

 an elevation of nearly fourteen thousand feet, while many of 

 them reach thirteen thousand feet above sea level. Here 

 again metamorphic rocks set in, containing indications of 

 metalliferous veins. Sedimentary beds, belonging to the 

 carboniferous and cretaceous ages the latter only on the 

 eastern slope, however rest against the metamorphic " core " 

 of the range. Volcanic eruptions of the trachytic series 

 have occurred, and show an arrangement parallel to the gen- 

 eral course of the chain. A more or less isolated group of 

 peaks lies north of Fort Garland, termed the Sierra Blanca. 

 Passes are both north and south of it Mosco Pass, and the 

 Sangre de Christo and Abeyta Passes. While cretaceous 

 beds overlying the carboniferous, and showing considerable 

 disturbances, slope off from the range toward the eastward, 

 their area is somewhat limited, as the lignitic group there 

 again makes its appearance in the Raton Hills and north 

 of them. LitholoGjicallv this is identical with the one ob- 

 served on the Rio San Juan. Comparisons of the succes- 

 sion of strata and relative thickness, etc., will be found in 

 the report for 1875. The age of this group has for some 

 time occupied the attention of geologists, and given occasion 



