SOIL AND SUBSOIL. 187 



occurrence of strongly calcareous or marly substrata, at depths 

 which in the humid region would not be reached by the roots, 

 but in the course of a few years are inevitably penetrated by the 

 roots of trees in the arid region. Then there appears a stunt- 

 ing of the growth, and sometimes a yellowing of leaves, or 

 chlorosis, due to the influence of excessive calcareousness at the 

 depth of four or five feet. For this of course there is no 

 remedy except the planting of crops which, like the mulberry, 

 Texas grapes, Chicasaw plum and others, are at home on such 

 lands ; which in the Eastern states are naturally occupied by 

 the crab apple, honey locust and wild plums. 



