374 SOILS. 



soon as the latter becomes decidedly calcareous; as is abun- 

 dantly exemplified in the loess or " bluff " formations border- 

 ing the Mississippi, Ohio, and Missouri rivers, where the black 

 walnut, tulip tree, ash, honey-locust, together with the lowland 

 oaks, hickories and cane usually characterizing the stream 

 bottoms, grow abundantly and with luxuriant development on 

 the adjoining steep hill country as well (see below, chapters 

 24, 2$). 



Soils of the Humid Region. Taking a view, first, of the 

 table showing the soils of the humid region, it appears that 

 the change of vegetation from walnut and hickory to the short- 

 leaved pine bears no visible relation to the increase or decrease 

 of potash or phosphoric acid, but is plainly governed mainly by 

 the amount of lime present. Where the short-leaved pine pre- 

 vails the soil is almost always either neutral or shows the 

 alkaline reaction in the course of half an hour; but where the 

 long-leaved pine predominates the soil has almost always an 

 acid reaction. The latter is also usually found in bottoms in 

 which the loblolly pine (P. taeda) prevails, and where, al- 

 though the soil may show a fair proportion of lime in the 

 analysis, it does not exist in the form of carbonate. 



The examples here given are from lands not derived from, 

 or underlaid by, limestone formations. Where the latter exist 

 the percentage of lime is usually materially increased ; as it is 

 also in the lowlands or bottoms when compared with adjacent 

 uplands (see above, chapter 10, p. 162; chapter 18, p. 331); 

 as well as in the delta lands of rivers. 



Soils of the Arid Region. Even a cursory comparison of the 

 soils of the arid regions of the Pacific slope with those of the 

 humid, as given in the above tables, shows some striking points 

 of difference. The most obvious is the uniformly high per- 

 centage of lime, and usually also of magnesia, in the arid soils, 

 and that quite independently of underlying formations, calcare- 

 ous or otherwise. This occurs despite the fact that while lime- 

 stone formations are very prevalent east of the Rocky Moun- 

 tains, they are quite scarce west of the same. The red (Lar- 

 amie) sandstones of Wyoming, the slates of the foothills of 

 the Sierra Nevada, the clay shales, granites and eruptives of 

 the Coast Ranges of California, Oregon and Washington, 



