GEOLOGICAL SURVEY OF THE TERRITORIES. 103 



and Columbus. The latter, from its supposed central geographical posi- 

 tion, has been regarded as the possible seat of the capital of the United 

 States in case of its removal to the West. 



Soon after leaving Columbus we cross Loup Fork or "Wolf Eiver, an 

 important branch of the Platte, which rises in the Sand Hills, one hun- 

 dred and fifty to two hundred miles to the northwest, and drains a large 

 area of country, in the summer of 1857 I had the opportunity of fol- 

 lowing it up from mouth to source in connection with an expedition 

 under the command of Lieutenant (now General) G. K. Warren, United 

 States Army. Its lower portion passes through an extremely fertile 

 region, but above the Pawnee Eeservation the Sand Hills begin to mo- 

 nopolize the country and render it unfit for settlement. 



We now pass the eastern shore of one of the most interesting and 

 most wonderful of those great lake basins which are found all over the 

 West from the Missouri Eiver to the Pacific coast ; there is no water 

 in it at the present time, and its existence is only known to the student 

 of geology. During the tertiary period it occupied an area of at least 

 one hundred thousand, and very possibly one hundred and fifty thou- 

 sand, square miles. It will thus be seen that our greatest northern 

 lakes, of which we so proudly boast, are but ponds in comparison with 

 some that once existed in this mountain region. The close observer 

 will notice at once that he is passing into a district the rock formations 

 of which are quite different from any that he has seen before. He finds, 

 also, that he is passing beyond the signs of great fertility, luxuriant 

 vegetation, fine farms, and fields of grain, to a comparatively arid, sterile 

 region; still, the broad bottoms of the Platte are covered with a fair 

 growth of grass, but the chances for the successful cultivation of .crops 

 of any of the cereals are very small. The soil becomes too thin, sandy, 

 and arid for the growth of anything more than a scanty vegetation. 



We might linger here for a moment and inquire into some of the 

 causes that have produced this scantiness of vegetation and almost 

 entire absence of trees over so large an area. There is quite a remark- 

 able belt or zone of country along the eastern base of the Eocky Mount- 

 ains, extending from the Arctic Sea far south to Mexico, upon which 

 but a small amount of moisture ever falls. This has often been denom- 

 inated the Great American Desert. In years past this belt was sup- 

 posed to comprise the greater portion of the area lying between the Mis- 

 souri Eiver and the foot of the mountains, but every year as we know 

 more and more of the country this belt becomes narrower and narrower, 

 and as a continuous area it has already ceased to exist, even in imagina- 

 tion. There are, however, large portions of the country that are com- 

 paratively worthless and arid, which may be called barren or sterile. 

 It is now pretty well understood that the cause of the absence of timber 

 in this great region is want of moisture. A very clear explanation of 

 this subject, and one which seems in accordance with the facts, is given 

 by Professor Dana in Silliman's Journal, vol. 40, page 393. If we were 

 to examine a rain chart we should find that where the forests are most 

 luxuriant, as along the Atlantic coast in the southern portion of the 

 Mississippi Valley, the greatest amount of rain falls annually — say fifty 

 to sixty-five inches ; and as soon as we approach any of the interior basins 

 of the western continent, or any portion of this dry belt, we observe that 

 the amount of moisture diminishes to thirty, twenty, fifteen, ten, and in 

 some cases to as low as five inches, annually. Again, along the Mis- 

 souri Eiver, where the vegetation is quite extensive and the forest trees 

 abundant, we have twenty to thirty inches of rain ; but as soon as we 

 pass to the westward three hundred miles we have but ten or fifteen 



