148 ORIGIN OF SCENERY OF BRITAIN 



points to the operation of some cause which, in 

 producing them, acted independently of and even m 

 some measure antagonistically to the present system 

 of superficial erosion. It is likewise evident that as 

 the lakes are everywhere being rapidly filled up by 

 the daily action of wind, vegetation, rain, and stream- 

 lets, they must be of geologically recent origin, and 

 that the lake-forming process, whatever it was, must 

 have attained a remarkable maximum of activity at a 

 comparatively recent geological epoch. Hardly any 

 satisfactory trace is to be found of lakes older than 

 the present series. How then have our lakes arisen ? 

 Several processes have been concerned in their for- 

 mation. Some have resulted from the solution of 

 rock-salt or of calcareous rocks and a consequent de- 

 pression of the surface. The ' meres ' of Cheshire, and 

 many tarns or pools in limestone districts, are examples 

 of this mode of origin. Others are a consequence of 

 the irregular deposit of superficial accumulations. 

 Thus, landslips have occasionally intercepted the drain- 

 age and formed lakes. Storm-beaches, thrown up by 

 the waves along the sea-margin, have now and then 

 ponded back the waters of an inland valley or recess. 

 The various glacial deposits boulder-clays, sands, 

 gravels, and moraines have been thrown down so 

 confusedly on the surface that vast numbers of hollows 

 have thereby been left which, on the exposure of the 

 land to rain, at once became lakes. This has undoubt- 

 edly been the origin of a large proportion of the lakes 

 in the lowlands of the north of England, Scotland, 

 and Ireland, though they are rapidly being converted 

 by natural causes into bogs and meadow-land. Un- 



