334 EROSION OF UNPROTECTED SOIL. 



plified by a comparison of tbe registers of the two stations of the Van 

 Diemen's Land Company. At Circular Head, a neck of hind which pro- 

 jects into the sea, clear of timber and under cultivation, it rains less 

 than at Woolnorth, also on the sea-coast, and equally exposed to the 

 north, but surrounded by a thick forest of luxurious growth.^ 



The climate of New South Wales and Van Diemen's Land is very dif- 

 ferent from what it was before these colonies were brought within the 

 pale of civilization. The destruction of thick herbaceous underwood 

 scruhbs and thick interwoven forests must have necessarily rendered the 

 climate drier. The 250,000 acres of cultivated land, freed from tbe bad 

 conductors of heat which covered them, have contributed toward the 

 increase of the mean annual temperature. The climate, though thus 

 drier and hotter, is far from being improved.^ 



EEOSION OF SOIL WHEN NOT PROTECTED BY VEGETATION. 



Allusion has already been made to the protection afforded by wood- 

 lands against erosion from rains, and the formation of torrents. Extreme 

 examples of these effects can nowhere be more strikingly observed than 

 in the interior of our continent, in the arid, and still for the most part 

 uninhabited, regions, where slender pinnacles of rock mark the former 

 thickness of strata, since removed, and cahons of immense depth afford 

 passage to rivers that once flowed near the surface. The study of these 

 wonderful results of erosion belongs to geology, and although, from the 

 presence of fossil wood in abundance, we know that forests existed in 

 these regions in the most recent of geological periods, and possibly 

 within the time that man has existed, we are wholly left to conjecture 

 as to their agency in retarding the ancient flow of waters, or the erosion 

 that may have followed their removal. We simply know that these 

 effects are comparatively recent, and that these processes are still going 

 on. But European experience has unhappily afforded abundant exam- 

 ples within the observation of the living, and still more, within the 

 period of historical record, more especially in the region of the Alps 

 and Pyrenees.' They are liable to occur wherever loose soil upon steep 

 slopes is exposed to rains, without the protection afforded by vegeta- 

 tion, and especially of woodlands. These damages, beginning with the 

 wearing of enormous chasms in the mountains, transport these materials 

 to the fertile valleys below, which they sterilize by covering the rich 

 alluvial soil with stones and gravel. The river- beds are raised and be- 

 come shifting channels, wholly unfit for navigation or other useful pur- 

 poses, and dangerous on account of the uncertainty of their changes, 

 when not confined between rocky banks; or if held between dikes, these 

 must be raised more and more every year, until sometimes, as in the Po, 

 the bottom of the river becomes raised above the level of the country 

 adjacent, and fearful inundations are threatened at every river flood. 



In an oflBcial report recently addressed by M. Bouquet de la Grye to 

 the Administrators of the Domains in Eoumania, the following conditions 

 of the valleys in that country from the effect of torrents are described, 

 and may serve to give an idea of the general manner in which these 

 agencies operate : 



1 Physical Description of New South Wales and Van Diemen's Land, by P. E. Strzecki, 

 pp. 192, 19:^. 



2/6., p. 239. 



'^ Abundant instances of destruction from this cause are given in the work of Mr. 

 George P. Marsh, entitled Man and Nature; and in his later work, The Earth as modified 

 ill Human Aciion. 



