xvin PREFACE. 



culture in regions where actual experience was either non-exis- 

 tent or very brief and partial. In the pursuit of these studies 

 he has been favored by exceptional opportunities, extending 

 over a varied climatic area reaching on the south from the Gulf 

 of Mexico to the Ohio, across to the Pacific coast, and to 

 British Columbia on the north. That a systematic investiga- 

 tion of soils over so large an area, covering both humid and 

 arid regions, should lead to some unexpected and novel re- 

 sults, is but natural ; and it is the discussion of these results in 

 connection with those obtained elsewhere, and with some of 

 the prevailing views based thereon, that must serve as the 

 justification for the present addition to an already well- 

 stocked branch of literature. 



From the very beginning of the scientific study of agricul- 

 ture, the investigation of soils with a view to the a priori de- 

 termination of their adaptation, permanent value, and best 

 means of cultural improvement, has formed the subject of 

 continuous effort. It is not easy to imagine a subject of 

 higher direct importance to the physical welfare of mankind, 

 whose very existence depends on the yearly returns drawn by 

 cultural labor from the soil. 



It is certainly remarkable that after all this long-continued 

 effort, even the fundamental principles, and still more the 

 methods by which the object in view is to be attained, are 

 still so far in dispute that a unification of opinion in this re- 

 spect is not yet in view ; and a return to pure empiricism is from 

 time to time brought forward to cut the Gordian knot. 



While this state of things is primarily due to the intrinsic 

 complexity and difficulty of the subject itself, it has unquestion- 

 ably been materially aggravated by accidental, partly historic 

 conditions. Foremost among these is the fact that until within 

 recent times, soil studies have borne almost entirely on lands 

 long cultivated and in most cases fertilized: thus changing 

 them from their natural condition to a more or less artificial 

 one, which obscures the natural relations of each soil to vege- 

 tation. 



The importance of these relations is obvious, both from the 

 theoretical and from the practical standpoint. From the 

 former, it is clear that the native vegetation represents, within 

 the climatic limits of the regional flora, the result of a secular 



