116 EFFECTS OF FOEESTS ON MOISTTJEE 



ages," says, — " In many parts of New England there are tracts, 

 many square miles in extent, and presenting all varieties of exposure, 

 which were partially cleared sixty or seventy years ago, and where 

 little or no change in the proportion of cultivated ground, pasturage, 

 and woodland has taken place since. In some cases, these tracts 

 compose basins apparently scarcely at all exposed to any local 

 influence in the way of percolation or infiltration of water towards or 

 from neighbouring valleys. But in such situations, apart from 

 accidental disturbances, the ground is growing drier and drier from 

 year to year, springs are still disappearing, and rivulets still 

 diminishing in their summer supply of water. A probable explana- 

 tion of this is to be found in the rapid drainage of the surface of 

 cleared ground, which prevents the subterranean natural reservoirs, 

 whether cavities or merely strata of bibulous earth, from filling up. 

 How long this process is to last before an equilibrium is reached, 

 none can say. It may be for years ; it may be for centuries. 



" Livingstone states facts which strongly favour the supposition 

 that a secular desiccation is still going on in Central Africa, and 

 there is reason to suspect a like change is taking place in California. 

 When the regions where the earth is growing drier were cleared of 

 wood, or, indeed, whether forests ever grew there, we are unable to 

 say, but the change appears to have been long in progress. A 

 similar revolution appears to have occurred in Arabia Petrsea. In 

 many of the wadis, and particularly in the gorges of the Wadi Feiran 

 and Wadi Esh Sheikh, there are water-worn banks showing that, at 

 no very remote period, the winter floods must have risen fifty feet in 

 channels where the growth of acacias and tamarisks and the testi- 

 mony of the Arabs concur to prove that they have not risen six feet 

 within the memory or tradition of the present inhabitants. Recent 

 travellers have discovered traces of extensive ancient cultivation, and 

 of the former existence of large towns in the Tih desert, in localities 

 where all agriculture is now impossible for want of water. Is this 

 drought due to the destruction of ancient forests, or to some other 

 cause ? 



" For important observations on supposed changes of climate in out* 

 Western prairie region, from cultivation of the soil and the introduc- 

 tion of domestic cattle, see Bryant's valuable Forest Trees, 1871, 

 chapter v., and Hayden, Preliminary Beport on Survey of Wyoming, 

 p. 455." 



Mr Marsh adds : — " Some physicists believe that the waters of our 

 earth are, from chemical or other less known causes, diminishing by 



