1874.] 283 [Allen. 



propose now to define is that of the Atlantic Slope, which will include 

 not only the country east of the Alleghanies, but a large part of the 

 British Possessions, extending westward at least as far as Fort Simp- 

 son, and thence northward and westward to Alaska, including, ap- 

 parently, all of that territory north of the Alaskan Mountains, with an 

 annual rain-fall throughout the whole of this extended region of 

 about thirty-five to forty-five inches. Over this region (to which we 

 may give the general term of Atlantic Region) the colors may be re- 

 garded as of the average or normal type, those of other regions being 

 either of a diminished or increased intensity. 



The second region will embrace the Mississippi Valley, or more 

 properly the Mississippi Basin, and may hence be termed the Mis- 

 sissippi Region. Here the annual rain-fall reaches forty-five to fifty- 

 five inches, and over a small area east of the Lower Mississippi even 

 exceeds sixty inches. The tendency here is so often to an increase 

 of fulvous and rufous tints, that we may regard this as the distinctive 

 chromatic peculiarity of the region, these tints reaching their maxi- 

 mum in the limited area of greatest humidity, but a general increase 

 in intensity of color is also more or less characteristic of the region. 

 A third region embraces the central portion of the Rocky Mountains, 

 and being developed most strongly within the present territory of 

 Colorado, and being also mainly included within that territory, may 

 be termed the Colorado Region. The tendency here again, as com- 

 pared with the immediately adjoining districts, is to a general increase 

 of intensity of color, with also a marked inclination to the develop- 

 ment of rufous and fulvous tints, this region being also within the in- 

 fluence of a comparatively high temperature, at least in summer. The 

 humidity is here less than in either of the other regions already de- 

 fined, the annual aqueous precipitation amounting to only about 

 twenty-four to thirty inches ; but it is yet greatly in excess of that of 

 the districts immediately surrounding it. 



The fourth region may be regarded as made up of the arid plains 

 and deserts of the great central plateau of the Continent, including 

 not only the " Great Plains," usually so called, but the deserts and 

 plains of Utah, Nevada, Western Colorado, New Mexico, Arizona, 

 and southwestward to Lower California, and may hence be appropri- 

 ately termed the Campestrian Region. The annual rain-fall is gener- 

 ally below fifteen inches, but ranges, at different localities, from 

 three inches to twenty. Here a general paleness of color is the 

 distinctive feature. The fifth region begins on the Pacific Coast 



