CHAPTER XXIV. 175 



It is questionable whether a numerical value can ever be satisfac- 

 torily established for the action of forests in direct increase of rainfall, 

 but it is believed that sufBcient has been advanced in the foregoing to 

 show beyond doubt that they do have an effect in that direction, the 

 matter of uncertainty being the question as tf quantity only. 



CONSERVANCY OF FORESTS. 



In the matter of conservancy of the water that has fallen, forests 

 play a very important part. They intercept the sun and rain, and save 

 the earth from packing hard under the baking of the one and the per- 

 sistent beating of the other. They appreciably decrease the quantity 

 that would otherwise pass rapidly off into the runs and waterways, 

 and be lost in floods. Not only do they lessen the wasteful and de- 

 structive expenditure of water in floods, but they afford greater time 

 for the earth to absorb to its full capacity the water held back by the 

 mechanical obstructions of the forest floor. They reduce the quantity 

 lost by evaporation. These things we enter on the credit side of the 

 forest account, and on the debit side make the sole entry of the water 

 used in supporting plant life. It remains to ascribe values to these 

 various items, and strike a balance. 



The effect of sun and rain in producing a hard ground surface that 

 sheds water like a roof is known to us all, and we equally know how the 

 broken surface of a ploughed field absorbs rain. The condition of the 

 ground surface is of first importance, and it is here that forests exer- 

 cise one of their most beneficent functions, a quality which in itself is 

 more than sufficient to justify our constant exertion in preserving and 

 extending our wooded areas. All permanent water supplies are drawn 

 directly or indirectly from the rainfall absorbed and stored within 

 the earth. Directly in the shape of wells, tunnels and infiltration 

 pipes. Indirectly through the medium of running surface streams, 

 which in turn draw their supply from visible springs and the unseen 

 accretions that come in along their beds from ground-water at higher 

 elevation. The surface water which flows into the streams after rains 

 gives but a temporary supply. The permanent flow comes from 

 ground-storage. It must not be thought from this that all ground- 

 water reappears at some time or other in the surface streams. Much 

 passes on unseen to the sea. Its place of discharge into the ocean Is 

 sometimes well marked. Off the east coast of England there is a sub- 

 marine valley, called the Silver Pit, twenty miles long and 50 to 250 

 feet in depth below the adjoining bed of the sea. The extraordinary 



