SOILS OF THE ARID AND HUMID REGIONS. 381 



" prairie soils " can question the fact ; which moreover is perfectly ex- 

 plicable upon the analogy already alluded to, with caustic lime, which, 

 together with caustic alkalies (potash and soda), is known to act power- 

 fully in the conversion of vegetable matter into humus. That instead 

 of liberating the nitrogen in the form of ammonia, as do the caustic 

 hydrates, the milder carbonate should only cause the formation of humic 

 amides, is quite intelligible. That such is really the case, has been 

 conclusively proved by the investigations of the writer made conjointly 

 with M. E. Jaffa (Rep. Sta. Cal. Agr. Expt. 1892-4) ; the general result 

 being that while in the humid region the average nitrogen-content of 

 soil-humus is less than 5 r / c , in the upland soils of the arid region 

 (where all soils are calcareous) that percentage rises as high as 22.0%, 

 with a general average of between 15 and 16%. That such highly 

 nitrogenous material can be more readily attacked by the nitrifying 

 bacteria than when a large excess of other oxidable matter is present, 

 is at least a legitimate presumption, especially in view of the very active 

 nitrification known to take place in the arid regions everywhere. So 

 long as a large excess of carbohydrates is present, the oxidation of these 

 will naturally take precedence over that of the relatively inert nitrogen. 

 The accumulation of the latter in the humus-substance of the arid 

 region, where oxidation of the organic matter of the soil is very active, 

 points strongly to this view of the case. 



Magnesia. While the differences in respect to the propor- 

 tions of lime are the most prominent and decided, yet the re- 

 lated substance, magnesia, shows also a very marked and con- 

 stant difference as between the soils of the humid and arid 

 regions. It will be observed that the general average for mag- 

 nesia in the soils of the Atlantic Slope is about double that of 

 lime; Florida and Rhode Island being the only states in which 

 the average is lower for magnesia than for lime. In the 

 arid region, on the contrary, magnesia on the general average 

 is nearly the same as lime; in the average by states, some- 

 what less; thus bringing the ratio for the two regions for mag- 

 nesia up to one to six or seven. This also is so decisive a 

 showing that no accident could bring it about. We must con- 

 clude that climatic influences have dealt with magnesia simi- 

 larly as witli lime; which from the standpoint of the chemist is 

 just what might he expected, since magnesia carbonate behaves 

 very much like that of lime toward carbonated waters. 



