268 



veg'etable tiud animal, what causes have brouolit in their present ap- 

 l)earances and habits, and how they may be made subservient to the 

 best uses of our people, render it necessary that large collections of 

 specimens, including all their varieties, stages of life, and peculiarities, 

 be amassed from all the varieties of surface, soil, water, and climatal or 

 chemical areas. 



Certain Eocky Mountain caiions and gorges which have been made 

 wider and deeper hj the forces. of nature, present level, or nearly level, 

 shelves, ridges, or plateaus, along the sides of the streams that dash 

 through them ; and the soil prepared there by the grinding floods and 

 decaying mineral masses has fitted up an abode for numerous creatures 

 which formerly could not live there. Other forms of life may have lasted 

 through less locally energetic changes of soil and surface from a time 

 that may date back far in some geological period of the past. 



The presence of Lihurnia vittatifrons (a salt-marsh form of the Atlan- 

 tic border in the warm-temperate zone) upon low spots in the prairies of 

 Illinois and Nebraska, may serve to show that these localities were once 

 the beds of salt-lakes. And may we not at least surmise that the extent 

 and boundaries of such, and of other formations of the past, may be 

 nearly determined by a careful search for the facts of distribution of 

 similar creatures. 



Why is it that the Elkhorn Cactus affects the plains and foot-hills of 

 Colorado south of the Divide, stopping almost suddenly in the vicinity 

 of Piiion, and scarcely, if at all, appearing north of this place? Three 

 of its allies, of less discrimination, extend over the whole length of the 

 plains, north and south, throughout the Territory of Colorado. 



The voracious grasshoppers, which come sweeping down from the 

 mountain-heights upon the plains, although identical in species over 

 hundreds of miles of territory, have well-marked races affecting differ- 

 ent sections, which make it easy for the practiced eye to distinguish a 

 southern form from one found farther north. 



A species of large sunflower grows on the plains of Kansas and Colo- 

 rado. In the latter State, it occurs in patches here and there, over a 

 distance of at least three hundred miles. Upon this sunflower, in the 

 valley of the Arkansas, lives abundantly the Gnathium minimum, Say ; 

 but north of this, the most rigid search failed to detect a specimen of it. 



Instances of similar import might be mentioned without number. But 

 I beg that you will pardon me for these few suggestions made in behalf 

 of the demands of modern science, and to encourage those who are 

 favorably situated to help in bringing together materials for a full his- 

 tory of the great region from which you have extracted so much that 

 conduces to the prosperity of our great country. 

 Very respectfully, vours, 



P. E. UHLEE. 



Dr. F, V. Hayden, 



CJiief of the tl. S. Geological and 



GeograxjMcal Survey of the Territories. 



