34 B^suM^ OF suebll'b study op 



of a vast ruin, and several torrents have obtained their names from a per- 

 ception of this resemblance. Thus is it with the torrent de la Eui-ne, at 

 Lantaret, the torrent de la Ruinasse, at Monestier, and the torrent de 

 Ruinance, on the Lower Alps. 



The deposit is a heap of pebbles and of blocks of stones, scattered over a 

 vast extent of ground — an arid region devoid of culture, of vegetation, and 

 even of vegetable soil — and it suggests to the mind the idea of some great 

 catastrophe having occurred. In sight of this enormous mass of debris, one 

 finds it difficult to perceive or admit that it can be the work of the paltry 

 thread of water — a mere streamlet — which is seen oozing thi-ough among 

 the rooks. Examined more carefully, it is seen that these heaps, which 

 seem scattered there in so much disorder, are disposed in accordance with 

 mathematical laws. 



The general outhne of elevation is that of a very much flattened hillock ; 

 the outline of shape is that of a half-expanded fan extending from the mouth 

 of the gorge and leaning on the mountain like a buttress. Projecting lines, 

 which mark on the surface of this cone the lines of greatest declination, are 

 arranged very regularly, following the gentle slopes, which bend inwards a 

 little towards the bottom, but maintain withal a perfect continuity,- — all 

 taking their departure from the mouth of the gorge forming the apex of the 

 cone. Further on they diverge somewhat further horizontally, with an 

 outline so distinct that if made with a ruler it could scarcely have been 

 more so, and thus is completed the resemblance first suggested — that of an 

 expanded fan, the joint of which is represented by the mouth of the gorge, 

 and the scales of the fan by these rays, somewhat raised towards the middle, 

 as is the back of an ass, and presenting an appearance such as may be 

 supposed to have been produced by the natural slope of a semi-fluid or 

 viscous body flowing out of the mountain and escaping by the gorge. 



The whole aspect of the mound is so peculiar that it reveals from a great 

 distance the existence of a torrent before any other indication has been seen 

 to awaken a suspicion that such may be there. It stretches often more 

 than three-quarters of a league in breadth, and its height above the level of 

 the vaUey may exceed 70 mtoes, or 230 feet. Nothing can better prove 

 the force of these torrents in action than those immense deposits formed 

 entirely of what has been ejected by them. 



When one looks, says M. SureU, at the slope presented by these beds of 

 deposits at the water level, following with the eye the central ridge of the 

 cone-shaped group of these, he may perceive them to manifest the following 

 three laws, which may be seen regulating the deposit beds of all torrents 

 reproducing the same or similar effects everywhere with the greatest con- 

 stancy : — (1) The longitudinal profile forms a continuous curve convex 

 towards the centre of the earth, — that is to say, to express the fact in other 

 terms, that the slope becomes less, diminishing in proportion as it goes 

 down towards the river ; (2) The changes in the declivity of the fall are 

 more rapid towards the top than towards the bottom ; (3) The declivity of 

 the fall, or slope, varies with the nature of the deposits. It is never under 

 2 centimetres per m6tre, nor above 8 centimetres — 2 and 8 in the 100 ; 

 and it is constant for all the torrents of the same locality, and which have 

 their origin in the same mountain range. 



It is then shown by the author that that cui-ve is the natui-al result of the 

 action of the flood ; and he proceeds to discuss the causes and the con- 

 sequences of the formation of these beds of debris deposited by them. 



