xin Action of Water on the Land 259 



by sharp stones is at the same time finely polished by the 

 clay, and thus acquires a highly characteristic appear- 

 ance. The general aspect of the smoothed and rounded 

 rocks is supposed to resemble the backs of sheep, hence the 

 peasants named them roches moutonnees^ i.e. sheep rocks. 

 The stones which took part in the polishing action, and 

 remain embedded in the clay, are themselves scratched and 

 smoothed in a similar way. The descent of a glacier in 

 a steep valley is believed by some geologists to give it an 

 impetus which causes the mass of ice to dig like a gouge 

 when it enters suddenly on flatter ground. To this gouge 

 action, strongest at the first shock, and then gradually 

 diminishing, the peculiar form of the rock -basins of 

 alpine lakes and fjords is usually ascribed. The deep 

 weathered crust ( 310) which forms on granite and other 

 hard rocks is readily scooped out, and its presence doubtless 

 helped in the formation of deep rock -basins. When the 

 climate admits of glaciers reaching the sea they give rise to 

 icebergs ( 234), and distribute their deposits far over the 

 bed of the ocean. At the end of a glacier on land the 

 ground moraine forms a ridge of boulder clay, and the 

 various moraine heaps carried along on the surface of the 

 ice are thrown down above it, producing what is called the 

 'terminal moraine. A diminishing glacier in a climate that 

 is growing warmer strews the whole valley, up which it 

 has retreated, with consecutive terminal moraines made up 

 of low hills of detritus. From the melting end of a glacier a 

 rapid stream of ice-cold water flows away, milky with mud, 

 which imparts to it great erosive power. The amount of 

 sediment removed by the Isortek River in Greenland from 

 the base of its parent glacier is calculated at 4,000,000 tons 

 a year. 



339. Rock -basins are usually long and narrow, and 

 attain a maximum depth, often of several hundred fathoms, at 

 a point about one-third of the distance from the head of the 

 basin, as shown in Fig. 5 5. The lakes occupying rock-basins 

 are characteristic of the valleys on the lower slopes of all 

 mountains which once bore great glaciers. By subsidence 

 of the coast-lands they form fjord-basins ( 229) filled with 



