72 DETAILED DESCRIPTION OF COMPARTMENTS. 



ture and condition of the soil. Their proportion is^roughly estimated 

 with the eye. In the last place, the nature of the subsoil exercises 

 a very marked influence on the forest growth, and may vary from com- 

 partment to compartment. The rock below may a,lso manifest its 

 influence on the topsoil above it by modifying its physical charac- 

 ters, according as its stratification is horizontal or inclined, or ac- 

 cording as it is compact or permeable, entire in sheet masses or 

 broken up. The physical characters of the topsoil, the chief of 

 which are stifiness or looseness, hygroscopicity and depth, always 

 exert a preponderating action on the forest growth. 



The state of division (looseness) of the soil, which is a product 

 of the nature and size of the particles composing it, goes on in- 

 creasing from stiff plastic clay that is impermeable both to air and 

 water, to loose sand and stones and agglomerations of rocks and 

 boulders. As regards hygroscopicity we have soils that are boggy, 

 wet, moist or dry. These classes of soils can often be recognised 

 by the characteristic species which grow on them ; but the humi- 

 dity of the climate and of the soil are to a certain extent comple- 

 mentary one of the other. 



Of all the characters of the soil, depth is generally that which 

 varies most from compartment to compartment, and is also the most 

 important. Thanks to it, the other characters perform their role 

 more effectively, the roots of the trees spread out and take a strono- 

 hold of the ground, the moisture of the soil is better preserved and 

 an excessive rainfall is more easily carried away into the depths of 

 the earth. Depth of soil is at once manifested by the form of the 

 trees ; in shallow soil the boles are short and the crowns low, with the 

 branches stunted and crooked, while in deep soil the boles are tall 

 and the branches of the crown straight and long. A soil possessing 

 a depth of 20in may be termed deep. Depth and the other charact- 

 ers of the soil may be observed in ditches, trenches, quarries and 

 cuttings, which open to the view a section of the topsoil traversed 

 by the roots of the trees. 



For any compartment in particular the soil is described in a few 

 words, and mostly by the use of comparative terms. The underly- 

 ing geological formation is not mentioned, unless it is different from 



