SOILS OF THE ARID AND HUMID REGIONS. 375 



and the varied black rocks of the great lava sheet of the Pacific 

 Northwest, all alike produce soils of high lime content as com- 

 pared with Eastern soils not derived from calcareous forma- 

 tions. This fact has already been referred to, but is more 

 fully illustrated in the table below. 



Aside from the lime-content, however, it will be noted in the 

 preceding table that the ^o/a^/i-content of the arid soils is on 

 the average considerably higher than in those of the humid 

 region. In fact it is hard to find west of the Rocky Mountains 

 (except where high elevation causes a humid climate) any 

 soils as poor in potash as are many of the commonly cultivated 

 lands of the Eastern United States. 



Other ingredients do not show such marked differences from 

 the purely chemical standpoint: yet, as will be shown below, 

 the forms in which silica and alumina occur are also not incon- 

 siderably modified. 



GENERAL COMPARISON OF SOILS FROM THE ARID AND 

 HUMID REGIONS OF THE UNITED STATES. 1 In order to 

 verify the conclusions just mentioned upon the broadest basis 

 possible, the following table has been compiled from all avail- 

 able sources ; partly published, partly in manuscript only, hav- 

 ing remained in the writer's hands since the cessation of the 

 Northern Transcontinental Survey, prosecuted from 1880 to 

 1883, under the auspices of the Northern Pacific Railroad, in 

 Washington and Montana. The published data are derived 

 partly from the records of State surveys, partly from the soil 

 work connected with the Tenth Census ; partly also from those 

 of Experiment Stations. In most cases it has of course been 

 necessary to restrict the comparison to such analyses as have 

 been made by substantially identical methods, for reasons al- 

 ready given ; but in the cases of some states from which numer- 

 ous analyses made by the Kedzie method, adopted by the As- 

 sociation of Official Chemists, w r ere available, the average has 

 been given but the name of the state starred, to indicate that 

 the percentages, excepting phosphoric acid, are lower than they 

 would be if made by the method adopted by the writer, par- 

 ticularly as regards potash. The adoption of the one-milli- 

 meter mesh for the fine-earth sieve instead of the half-milli- 



1 Abstracted and revised from Bulletin No. 3, U. S. Weather Bureau, 1893. 



