328 LIFE IN THE ALPS. 



the mountain-slopes around my chalet we sometimes ob- 

 serve little valleys, or couloirs, as the French call them, 

 where the stones and boulders lying on the surface are 

 more crowded together than elsewhere. They follow 

 each other so as to suggest the notion that they are 

 moving in a regular stream down the couloir. But 

 when we observe them closely from year to year, we 

 cannot find the slightest evidence of the sliding of the 

 stones. Walking over the hills, we soon detect another 

 fact which proves that though no trace of slipping can 

 be observed, a movement of the stones downward does 

 undoubtedly take place. To prove this I take you to a 

 grassy slope, with a great number of boulders strewn 

 over it. I select one of the largest of these, a boulder 

 thirty or forty tons in weight, and ask you to look 

 closely at the slope behind it. For a considerable dis- 

 tance, say one hundred yards, upwards there is a grass- 

 covered furrow corresponding in width to the size of the 

 stone. Look now to the front of the boulder. Sods 

 and smaller stones are piled up in front. You cannot 

 resist the conclusion that the furrow behind marks the 

 track along which the boulder has moved, and that the 

 sods and stones in front have been pushed up by the 

 boulder in its descent. Turning to other stones in the 

 neighbourhood, we find them all, more or less, in this 

 condition. The whole crowd of stones is, in fact, 

 moving slowly down the slope of the mountain. And 

 yet, even by the closest scrutiny, you can never find any 

 trace of fresh earth which the stone has recently quitted. 

 The growth of the grass appears to be as quick as the 

 motion of the boulder, thus destroying all obvious 

 evidence of mere sliding. 



I do not myself doubt that the motion takes place 

 mainly in the spring, when the melting snows render 

 the soil upon the slopes particularly soft and yielding ; 



