242 SECTIONAL ADDRESSES 



profile is the soil unit which must be studied as a whole, unmodified by 

 artificial operations of man. This of course introduces difficulties in old 

 settled countries of dense population, like our own, where most of the soils 

 which are worth cultivation have been broken up and cultivated at one 

 time or another. In the extensive, lightly populated areas of Russia or 

 North America there are plenty of natural soils, but in applying modern 

 methods of soil study to the soils of much of Western and Southern 

 Europe and other regions of ancient civilisation, modifications have to be 

 introduced to allow for the influence of cultivation which, in many cases, 

 extends over long periods of time. 



There is another difficulty which, it seems to me, has not received the 

 consideration it deserves. Soils are divided in this system into mature 

 and immature, called by those who rejoice in using Greek words unknown 

 to the vulgar, Ektodynamomorphic and Endodynamomorphic soils 

 respectively. A mature profile is one which has attained its full develop- 

 ment, while an immature profile has not attained its full development. 

 But when is this full development attained ? Certain of the soil-forming 

 processes require a very long period for their full development, others a 

 much shorter period. Some processes require periods of geological time, 

 others can take place in a few years or a few centuries. 



The late Mr. George Newlands and myself studied a few years ago the 

 mineralogical composition of certain Scottish soils, and found that our 

 granitic soils, for instance, are largely composed of the minerals of the 

 original granite in an unweathered or only slightly weathered condition. • 

 Much of the ' fine sand,' technically particles of approximately o • 2 to o -02 

 millimetres in diameter, consists of almost unweathered particles of 

 orthoclase, muscovite and other compound silicates and not merely of 

 quartz. These are found not only in the parent material a few feet below 

 the surface but in the surface layers which have been undergoing chemical 

 processes of weathering as long as the soil has been there. 



The parent material of these soils is glacial detritus powdered down by 

 ice and left behind when the ice melted after the last glacial epoch. How 

 long is that ago ? I leave that question to be answered by Section C. 

 At any rate it is a long time ago, before human history started in Scotland. 

 But as the pedogenic processes in these soils are not complete in this 

 respect, the profiles, ex hypothesi, cannot have attained their full develop- 

 ment and therefore are still immature. But many of such soils have 

 profiles which are treated as mature. 



Soil organic matter, on the other hand, is subject to rapid change and 

 decay especially in a warm climate. Even in our cool climate humus is 

 rapidly formed under suitable conditions. So far as the organic matter 

 of the soil is concerned it rapidly comes into a condition of equilibrium 

 with the conditions prevailing, and so far as it is concerned the pedogenic 

 process is completed in a comparatively short period of time, though a 

 change in the conditions may throw it out of equilibrium again for a time. 



The whole of the processes of soil formation are very complex and require 

 much more study before we can hope to reach, I will not say a final, but a 

 sound system of soil classification. The soil itself is, from every point 

 of view, a very complex and variable material and our present methods 



