LETTER OF THE GEOLOGIST. XIX 



few proinineut points, or in a high mountain country, it would probably 

 be of little or no use. Altitudes were determined by the mercurial ba- 

 rometer, with a base at the White Eiver Indian agency, and checked by 

 a continuous system of vertical angles. The altitude of the agency has 

 been determined by a series of barometric observations extending over 

 two years and a half, and referred to railroad levels, and can probably 

 be depended on to within a few feet. The altitude of the agency being 

 about 0,500 feet, and the altitudes in the district ranging from 5,000 to 

 8,000 feet, makes its location the best possible in height for a barometric 

 survey of the region. 



It is the intention of the survey, during the coming year, to publish 

 some tabulated results of the barometric work in Colorado, showing the 

 system and its accuracy and reliability. This may be of use in future 

 work, since the topography of the whole west must greatly depend on 

 barometric determinations of altitude, and Colorado has furnished almost 

 every possible phase of western topography. 



The longest dimension of the work lying east and west, and the White 

 and Grand Eivers running in approximately parallel courses, the dis- 

 trict stretched from the White Eiver up over the divide between the 

 Grand and White, and embraced the heads of the lateral drainage of 

 the former river. 



The general topography is a gentle rise from the White Eiver toward 

 the south, and a sudden breaking off when the divide is reached into 

 rugged and often impassable clift's, known on the maps as the Eoan or 

 Book Mountains. The gentle plateau slope of the White Eiver side is 

 cut by almost numberless and often deep caiions, and in many cases the 

 surface of the country has been eroded away, leaving broken and most 

 picturesque forms, the lower benches generally covered with cedars and 

 piuons, and the upper rich in grass. 



There are four main streams draining into the White Eiver within the 

 limits of our work — a distance of something over 100 miles. The eastern- 

 most is a large running stream ; the second, though tolerably good water 

 may be found in pools in its bed, carries in the summer no running 

 water for the greater i)art of its course ; the third has for most of its 

 length a trickling stream of the bitterest of alkali water, while the fourth 

 and westernmost one is perfectly dry for some twenty-five miles from its 

 mouth, and then forks, one branch containing pure, sweet water in pools, 

 the other a running stream of bitter alkali. All of these streams have 

 more or less good water at their heads. The party traveled nearly the 

 whole length of all these water-courses, but found good trails only in. 

 the two middle ones. Trails, which traverse the whole district in every 

 possible direction, keep mostly on the summits of the ridges and plateaus, 

 and by taking care not to cross the caiions, the country is very easily 

 traveled through. 



The country is almost entirely destitute of timber, and has but little 

 good water. It is, however, abundantly supplied with grass, and, espe- 



