ASSESSMENT OF THE LOCALITY. 49 



coloured for a long time, blackish colour which disappears on 

 roasting ; iron by red colouring, etc. 



In order to recognise more easily the principal constituents 

 of a soil and their proportion, a sample may be mixed in a 

 glass tube with about twice its volume of water, well stirred 

 until completely dissolved, and then allowed to settle. At 

 the bottom of the glass tube the following deposits will be 

 observed, beginning with the low^est : — 



First : The rougher grains of sand. 



Second : The finer grains of sand. 



Third: Lime, chalk and the coarser clay. 



Fourtli : The finer clay and particles of humus. 

 The thickness of the layers indicates the proportion of each 

 substance. 



In spite of the most persevering attempts, experience has 

 shown that the assessment of the locality in the manner 

 indicated above is always subject to grave errors, because the 

 various factors may compensate each other, replace one 

 another, or may be altogether unassessable. To make 

 matters worse, the factors are rarely the same over exten- 

 sive areas, but change from one spot to another. On the 

 whole, the method which has just been indicated can only 

 serve as a make- shift when no better means of assessment 

 are available, or as a help in the application of the method 

 now to be described. 



2. Assessment oj the Loecdity according to a Crop of Trees 

 prodiiccd hy it. 



When a locality has already produced a crop of- trees, it 

 may be assumed that, unless extraordinary events or irregu- 

 lar treatment have interfered with the development of the 

 trees, the effects of all its factors have found due expression 

 in such crop, which is therefore the best guide for the as- 

 sessment of the quality, or yield capacity, of the locality. 

 If, for instance, an acre of ground has produced a total 



s. t; 



