4 Remarks on the Formation of Alluvial Deposites. 



it. If the loosened strata fall into a valley, a large part of the 

 fragments is thrown across its bottom, and even to a consider- 

 able distance up the opposite declivity ; so that the appearance 

 of the ruin is that of an enormous wave, rushing down one side 

 of the valley, dashing up the other side, and there arrested and 

 fixed. 



, Another circumstance, by which we may recognise the ex- 

 istence of a landshp, is, that the large fragments are often com- 

 posed of several strata ; whereas, by the more gradual processes 

 of disintegration, hereafter to be described, the strata are always 

 cleft asunder, and the form and size of the fragments is determin- 

 ed by the structure of separation of the parent rock, which is sub- 

 divided as minutely as is conformable to that structure. While 

 going through the pass of the Gemmi, in the Canton of Valais, 

 where it borders upon the Canton of Berne, I observed, amidst 

 the extensive ruins of a landslip, numerous masses of thinly 

 stratified limestone, bounded on four sides by cleavages perpen- 

 dicular to the planes of stratification, and hence bearing a strong 

 resemblance to square towers of mouldenng masonry. These 

 masses are thrown on every side in wild confusion, often lying 

 prostrate upon the ground. 



The fall of mountain masses across valleys sometimes pro- 

 duces lal-csy by arresting the water flowing from above. The 

 Oschenen-see in the Canton of Berne is a fine example of such 

 a lake. It occupies the head of a narrow valley, and is over- 

 hung by lofty mountains, the perpendicular sides of which con- 

 stitute its eastern boundary. Several cascades fall immediately 

 into it from the impending snows and glaciers. The dam, 

 thrown across the valley so as to form the western boundary of 

 the lake, consists of loose angular masses of limestone ; and, on 

 looking up to the mountain on the south, we see, directly above 

 the dam, the smooth surface of a stratum of limestone, totally 

 cleared of its former burthen of earth and rocks, and inclining 

 towards the valley. A considerable part of the dyke is now 

 covered with fir-tre?s, which prove the ancient date of the slip, 

 although the cleared and sloping stratum above remains desti- 

 tute of vegetation, in consequence of its great height. The 

 water of the lake escapes through the broken masses of the 

 dyke. Rather turbid, as it enters, it emerges in numerous 



