and Suhterranean Water Storage. 77 



the mineral carbonate of lime is the same, in one case the 

 atoms are arranged with perfect symmetry to form a tran- 

 sparent crystal, in the other they have been bound tog-ether 

 by laws of structure and by the presence of life. This is only 

 one example out of many. Change in all respects is the rule, 

 and not the exception, in all those deposits originally made in 

 water, and now forming part of the earth's crust. The laws of 

 this change are among the discoveries that may be looked forward 

 to with confidence, but at present they are imperfectly tmder- 

 stood. 



Thus, then, it appears that water exists, and is in constant 

 circulation through the earth ; that, of the rain that falls, a cer- 

 tain proportion entering the various rocks and strata is em- 

 ployed in helping this process. The operation goes on inces- 

 santly. It is not easy, nor indeed always possible, to determine 

 where these surfaces of partial or absolute saturation may be. In 

 every district a knowledge not only of the surface, but of the 

 structure of the earth is necessary. In England the geologically- 

 coloured maps of the Ordnance Survey afford an easy and ready 

 means of applying general geology to local peculiarities, and 

 learning as nearly as possible where the subterranean water 

 channels exist, how they may be exhausted, and whence they 

 might be replenished. 



IV. — Effects of Clearing, Cultivation and Drainage 

 ON Water Supply. 



Water supply, derived from the clouds, distributed by rain, 

 and afterwards returned to the sea by the aid of streams or 

 utilised by organic structures, depends on the lorm of the 

 land, the extent of adjacent land, the vicinity to mountains or 

 ocean, the form of the mountains, much more than on latitude 

 and longitude. It is modified also by the state of cultivation 

 of the land, the extent and nature of forest and other vegetation, 

 and the rapidity with which the rain that falls runs off or is 

 absorbed into the surface, as I have already pointed out. 



The greater part of the land of the temperate zones, as Avell as 

 within the tropics, was formerly covered with dense forest 

 wherever circumstances were favourable for vegetation. Many 

 districts less favourably situated for such vegetation than Eng- 

 land are still covered with timber, and there are many parts 

 of the continent now absolutely bare where dense forests have 

 existed not long ago. Besides historic proof of this, in many 

 cases there is also the evidence of our senses seen in the innu- 

 merable branches, trunks, and roots of trees, dug up in old 

 turbaries, in boggy tracts on mountain sides, and at the mouths 



