74 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 
and complex series of changes that the minerals of the rocks 
become transformed into soluble matters which are adapted for 
plant-food and the insoluble matters which form the basis of the 
soil, The farmer, by the process of tillage, can facilitate those 
changes, and modify in some measure the natural processes. But 
the growth of the forest is slow, and the forester must rely in 
a far greater degree on the slow operations of nature for the 
nourishment and growth of his trees. A knowledge also of the 
conditions which favour the preservation of the soil when formed, 
and prevent its removal by running water and other agencies, 
will in many cases be of value. The growth of the forest in 
itself greatly promotes the accumulation and preservation of the 
soil, while the rapid deforesting of a district may result in such 
injury that the subsequent growth of trees may be rendered 
almost impossible. 
In another way, also, the nature of the underlying rocks affects 
the forester, for some are loose and open, others, such as boulder 
clay, are compact and almost impenetrable. Such rocks prevent 
the downward passage of the surplus water from the soil. They 
are damp, cold, and stiff, and require artificial drainage. They 
offer such resistance to the progress of the roots as greatly to 
hamper the growth of trees after a certain size has been attained. 
This influences also the holding power of a tree, and the ease 
with which it will withstand a storm. 
The geologist, by his study of a district, is often in a position 
to offer useful advice on questions of water supply. The drainage 
of water from the soil depends on the nature and structure of 
the underlying rocks, and this determiaes also the possibility of 
obtaining water supplies by boring. The underground circula- 
tion of water depends on circumstances which only a careful 
geological examination can bring to light. 
Other questions, to which I shall only briefly refer, as in- 
fluencing opinion as to the geological forces at work in any 
area, are situation and exposure, prevalent winds and rainfall, 
exposure to frost, to floods, and to storms; and the importance 
to the forester of the accurate knowledge of such conditions as 
these can hardly be overestimated. 
Joun 8. Fiert, M.A., B.Sc., M.B., C.M., 
Honorary Consulting Geologist to the Society. 
