274 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



that of Mi 1 . Wilson for the same year. The rocks here are 

 trachytes, interlaminated with tuffs in horizontal layers. 

 They rest partly on metamorphic rocks and partly on the 

 remnants of cretaceous sandstones. Previous to the out- 

 pourings of these trachytes, the country was evidently sub- 

 jected to considerable erosion, the sandstones being in many 

 places entirely removed, exposing the gneissic rocks upon 

 which they were deposited. Going westward toward the TJn- 

 compahgre River, the volcanic rocks disappear, and rocks of 

 upper cretaceous age show in bluffs on the east side. The 

 weathering of these beds has produced a barren alkaline soil, 

 in which there is no vegetation. In the immediate river 

 bottom there is some good soil, but it is limited in extent. 

 The course of the Uncompahgre is a few degrees west of 

 north, and between it and the drainage of the San Miguel 

 and Dolores Rivers, which has, approximately, the same di- 

 rection, is a plateau-like country with a gentle slope to the 

 eastward toward the Uncompahgre, and breaking off in 

 benches on the Dolores side. Seen from the mountains, this 

 plateau appears very regular, nevertheless it is very much 

 cut up by numerous canons, which carry water only in wet 

 seasons. The floor of the plateau is composed chiefly of 

 sandstone of the Dakota group (Cretaceous No. 1), underlaid 

 by Jurassic shales and red beds (triassic?), which rest upon 

 metamorphic rocks, as seen in the canons. On the western 

 side of the plateau is a monoclinal fold, which in some places 

 becomes a fault of 300 to 500 feet. 



One of the most curious features of this region is a canon 

 extending from the Dolores River to the Gunnison River. 

 It is evidently the bed of an old stream, which probably 

 once flowed toward the Gunnison. At present there are in 

 it two creeks, one a tributary of the Gunnison, and the other 

 a branch of the Dolores, the latter the principal stream of 

 the two. At the divide between them the canon is about 

 1200 feet deep, 900 feet of gneissic rock and 300 of sediment- 

 aries on the top. The dip is toward the east, and the creek, 

 flowing in that direction, gradually gets higher and higher 

 in the schists, and finally cuts through the overlying sand- 

 stones in which it joins the Gunnison. Toward the west the 

 canon rapidly increases in depth, until it is 3000 feet below 

 the crcneral surface. The stream on this side cuts across the 



