HISTORICAL 



33 



Such regions are rainless, usually sandy, and commonly not habitable." 

 Another characterizes a desert as "A region of considerable extent 

 which is almost if not quite destitute of vegetation, and hence unin- 

 habited, chiefly on account of an insufficient supply of rain : as. the 

 desert of Sahara ; the Great American Desert. The presence of large 

 quantities of movable sand on the surface adds to the desert character 

 of a region. The w^ord is chiefly and almost exclusively used with 

 reference to certain regions in Arabia, and northern Africa and others 

 lying in central Asia. The only region in North America to which 

 the word is applied is the Great American Desert, a tract of country 

 south and west of the Great Salt Lake, once occupied by the waters of 

 that lake when they extended over a much larger area than they now 

 occupy. The name Great American Desert was originally given to 

 the unexplored region lying beyond the Mississippi without any special 

 designation of its limits" (Fig. 2). 



The insufficiency of the above descriptions obviously rests upon faulty 

 observations, and upon the failure to recognize the fact that the habita- 

 bility of a region is no criterion of its arid character. The development 

 of modern methods of transportation has made possible the maintenance 

 of dwellings and towns with a considerable population at one or even 

 two hundred miles from the nearest supply of water. Even such facil- 

 ities are not necessary to the sustenance of a population in deserts of the 

 most extreme type as illustrated by the Sahara which has a popula- 

 tion of two and a half million people. So far as the vegetation is 

 concerned the actual number of individuals is much less than on a sim- 

 ilar area in a moist climate ; this in fact is one of the chief characteris- 

 tics of a desert, but it would not be safe to estimate the total number 

 of species much below the average number. Lastly, be it remembered 

 that local topography has but little influence on the desert character of 

 a region. Sandy flats, plains, valleys, and rocky hills reaching to such 

 altitudes as to become mountains are included in some desert tracts. 

 It follows as a natural consequence of the sparse vegetation as one 

 factor, that the surface layers of the substratum, being usually dry in 

 arid regions, are readily shifted and worn by winds. 



The designation of the vast region between the Missouri river and 

 the Rocky mountains as the Great American desert rested upon a lack 

 of definite knowledge by the earlier geographers, which was shown by 

 text books as recently as 1843. Later, when the more exact results of 

 the earlier explorations and surveys became known, the more important 

 arid regions were fairly well delimited and the desert areas in the Bad 

 Lands, the Staked Plains of Texas, the Chihuahua desert, the Great 



