19"] STEVENSON— FORMATION OF COAL BEDS. 531 



tected by a thin layer of turf, is denuded with extreme slowness 

 except along the lines of its watercourses. Indeed, the evidence is 

 wholly clear to every one who has crossed Scotland by way of the 

 Caledonian canal, which utilizes a chain of small lakes, fed by streams 

 rising in the Highlands and descending with rapid fall. The lakes 

 are not turbid, they rarely show blocks or chunks of peat where the 

 streams enter, the only evidence of vegetable matter being coloration 

 of the water by salts of organic acids leached from the peat. The 

 same condition exists elsewhere in Scottish lakes. 



Many years ago. Marsh" wrote elaborately respecting the pro- 

 tective influence of vegetation and the disastrous consequences fol- 

 lowing removal of forests. He recognizes that humus can absorb 

 almost twice its weight of w-ater, which it surrenders to the under- 

 lying soil and becomes ready to absorb more. Twigs, stems, fallen 

 trunks and the rest oppose the rush of water and break into small 

 streams any larger ones formed by union of petty rivulets. He cites 

 many works, reporting official as well as private studies — all record- 

 ing the same results. 



In the French Department of Lozere. which was among those 

 most seriously injured by the inundation of 1866 — caused by rains, 

 not by melting snow — it was remarked everywhere that " grounds 

 covered with wood sustained no damage even on the steepest slopes, 

 while in cleared and cultivated fields the very soil was washed away 

 and the rocks laid bare by the pouring rain." Marsh cites Foster, 

 who describes an area with slope of 45 degrees, which consisted of 

 three sections : one, luxuriantly wooded, with oak and beech from 

 summit to base ; a second, completely cleared ; a third, cleared in 

 the upper part but retaining a wooded belt for one fourth of the 

 height from the bottom. The surface rose 1,300 to 1,800 feet above 

 the stream flowing at the foot. The first section was wholly un- 

 scarred bv the rains ; the second showed three ravines, each increas- 

 ing in width from summit to base ; while the third, of same superficial 

 extent, had four ravines widening from the summit to the wooded 

 belt, in which they became narrower and soon disappeared. He 



" G. P. Marsh, " The Earth as Modified by Human Action," New York, 

 1874, pp. 232-238. 



129 



