TERRACES IN SWITZERLAND. 41 



From Geneva I turned eastward and followed the Arve nearly to its source, on 

 the route usually taken to Chamouny. On looking over Mr. R. Chambers' paper 

 on the valleys of the Rhine and the Rhone, since my return home, I find that he 

 took the same route, and has anticipated some of my observations. I shall, how- 

 ever, give the few which I collected as they appeared to me. 



At the south end of Lake Leman, where the Arve from the region of Mont 

 Rlanc unites with the Rhone, a mile below Geneva, as it comes from the lake, is 

 a deep accumulation of detritus, through which both the rivers have worn a 

 passage. It was mainly brought down by the Arve, a rapid and tumultuous 

 stream, almost always loaded with matter mechanically suspended. It is in fact the 

 delta terrace of that river and the Rhone, and extends back to the Saleve Moun- 

 tains. A mile or two east of the city we reach its highest part in that direction, 

 before crossing the Sardinian frontier. I found the terrace there to be 137 feet 

 above the lake. Passing from this level towards the Arve, we find one or two 

 lower terraces : which are composed of pebbles and boulders mixed with clay, not 

 unlike the "boulder clay" of Scotland. 



There can hardly be a doubt that Lake Leman owes its existence to this delta 

 terrace of the Axwe. But this point will be better understood when I have treated 

 of analogous cases in my paper on Erosions. 



As we proceed along the Arve towards its source, we find terraces more or less 

 distinct most of the way to Sallenches, which is 36 miles from Geneva. These 

 terraces for the most part slope with the stream, and they, also, usually slope 

 towards the river, often rapidly, so as to form the Glacis Terrace. ' In some places, 

 especially where the valley is narrow, there is only a single slope, as is very com- 

 mon in the higher Alpine valleys, where the river runs at the foot of one of the 

 hills. 



The materials of the terraces are usually coarse, though sometimes we pass 

 alluvial meadows. But the higher terraces are very coarse, often like unmodified 

 drift. A few miles below Bonneville, I measured a terrace, not the highest, and 

 found it 314 feet above Leman, 1544 above the ocean, and about 134 above the 

 Arve. A little beyond Bonneville, I measured another, which was 372 feet above 

 Leman, and 1603 above the ocean. At Sallenches, I found one which is 581 feet 

 above Leman, 1811 above the ocean, and about 120 above the "Arve. Around 

 Sallenche the terraces are fine, but on the north side of the river I suspect the 

 existence of a portion of a former terminal moraine. Still lower on the stream I 

 thought I discovered another, and when we had gone a league or so beyond St. 

 Martins, and began to ascend the enormous masses of coarse detritus unmodified, 

 I could not doubt that we had reached the terminal moraines of former glaciers. 



Four or five miles before reaching Chamouny, we pass a long and narrow defile, 

 and as we might have expected, found terraces above where the valley opens, in 

 which Chamouny is situated. A few of them may be level-topped; but they 

 mostly slope rapidly towards the Arve. Chamouny (Union Hotel), according to 

 my barometer, is 3270 feet above the ocean : 3425, according to Johnston's Dic- 

 tionary of Geography, and 3190 French feet, according to Keller's map. 



Some distance above Charnomvy, and just beyond the termination of the Mer de 

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