Obtuse Cones and Sectors on Shores of Lakes. 35 



meter, and partly covered with coppice-wood, is formed in the 

 Lungern-see, by the depositions of a small river flowing from 

 the head of the valley. This obtuse cone extends a few feet 

 under the water, and is then suddenly cut off by the steeper 

 declivity of the acute cone, which descends to the depth of about 

 20 feet, and is seen to be strewed with fallen sand and pebbles 

 as far as the eye can reach. A semicircle of surprizing mag- 

 nitude is exhibited, where the Kander dischai'ges itself into the 

 lake of Thun, through an artificial channel, opened A. D. 1712. 

 Within this time, an alluvial area has been formed of about 200 

 acres. From the shallows along its border, the lake deepens 

 suddenly to 600 feet. The border advances several yards in 

 almost every year. A work of the same kind was executed a 

 few years ago in the Canton of Glarus for the purpose of dis- 

 charging into the Lake of Wallenstadt the materials brought 

 down in overwhelming quantities by the Linth. In these and 

 similar cases, the newly formed area is in parts covered with 

 various kinds of willow, alder, hypophae, berberis, or viburnum, 

 and in other parts gemmed here and there with the brilhant 

 colours of a solitary alpine plant, the seeds of which have been 

 brought by the waters from the high mountains. 



It is evident that the complete semicircle. Fig. 24, can only 

 be formed where the stream intersects a straight bank at right 

 angles. But the greatest streams, which flow into lakes, com- 

 monly pass through valleys, which become lakes wherever the 

 water is detained by a barrier. The sides of a lake, therefore, 

 commonly converge in the direction from which the main stream 

 flows, so that, instead of a semicircle, it forms only the sector 

 of a circle, Fig. 26, dipping, as before, under the water, and 

 then passing into a steep declivity. In this state things are 

 found at the head of nearly all great lakes. The advance of 

 the area c c, formed by the depositions at the head of the lakes 

 of Geneva, Lucern, Neuchatel, Constance, Wallenstadt, and 

 many others, is both attested by historical records, and is the 

 subject of personal observation. In all these cases, as the arc 

 which terminates the river advances, the older portion of its bed 

 is continually brought nearer and nearer to an exact level, and 

 becomes liable to all the changes described in the second part of 

 this paper. 



c2 



