80 



KEV. A. IKYINGf ON THE 



Mims, in Graubiindten. It forms a mountain 600 metres high, and 

 extends from near Ilanz to Reichenau, in the Yorder-Rhein Thai. 

 Upon its surface eight small lakes are found. The Rhine and its 

 tributary streams have sawn it out into a number of hills which 

 abut as spurs upon the valley ; and at the present time above Ilanz 

 there are still visible traces of the ancient lake which was formed by 

 the waters of the Rhine as the valley was blocked up by the Fels- 

 sturz of Flims. Upon the back of this huge mountain of debris 

 there are traces of glacier-moraines and enormous blocks from the 

 Puntaiglas Thai. This Bergsturz is therefore older than the period 

 at which the moraine-materials were spread upon it — that is, older 

 than the glacial period." A few smaller lakes formed by Bergstiirze 

 were observed by me last summer near the Pirn Pass in Tyrol ; but 

 I am not aware that they have been yet described anywhere. 



(7) Lastly, there is the action of diluvium in blocking up valleys. 

 This fact must be so familiar to all Alpine travellers as to need no 

 proof here. In many cases the materials have been more widely 

 distributed, so as to form alluvial deltas, of which I have noted a 

 score or two of instances, at points where two valleys converge. In 

 other eases the diluvial detritus remains piled up in huge chaotic 

 masses at the mouth of a gorge opening laterally into a valley. I 

 saw such a recent accumulation only last summer, near Solden, in 

 the Oetz Thai ; and Credner* relates an instance which happened in 

 the year 1818, in the Bainen Thai, in which a mass of debris 100 

 metres high was accumulated at the mouth of the gorge, some of the 

 transported blocks of granite measuring 40 cubic metres. Sudden 

 and great downpours of rain in Alpine regions, or the rapid melting 

 of snow by the warm dry wind known as the Fohn, may furnish 

 the rushing waters. Collected from an extensive and steeply sloping 

 basin high in the mountains, and driven with enormous velocity 

 downwards, as through the narrow neck of a funnel, the transport- 

 ing power of water becomes enormous, while the rock-materials, 

 being only generally of a specific gravity of 2-00 to 2*90, lose nearly 

 one half of their weight in water. As soon as such a powerful cur- 

 rent escapes from the confines of its narrow channel, its velocity of 

 forward movement is again diminished, and it deposits its burden 

 near the mouth of the gorge as chaotic masses of stones or as mud- 

 streams. In time all the smaller stones and earth get spread out 

 as deltas, which in numerous cases are seen protruding into lakes 

 already formed, and in some instances have actually divided a lake 

 into two, as is the case with the Plansee, and with the more notable 

 instance of Lakes Brienz and Thun. Some instances of enormous 

 work done in this way, as the result of a single storm, have come 

 under my own observation. The side valleys which pour their 

 water and rock-debris in this way into another valley are often of 

 younger date than the principal valley : they may be seen in all 

 stages of recession from older valleys in the Alps. Difference of 

 composition and the strike of the strata may also help to forward 

 disintegration along some lines rather than along others. The one 

 * Elem. d. Geol. p. 222. 



