Vol. 54.] THE STRUCTUEE OF THE DAVOS VALLEY. 285 



serpentine in situ on the Schwarzsee Alp is ^ mile distant, and thus 

 there is everj'- reason to suppose that the real rock-floor lies far 

 below the present stream-bed. 



Turning now to the southern end of the area, we find the mouth 

 of the Sertig Thai marked by scenic features readily noticed by the 

 least observant eye. On the eastern side are two great flat- topped 

 terraces, the Wildboden and the Junkersboden, which present to 

 the west a very steep bank more than 100 feet in height. They 

 are separated by the Sertig Bach, which has cut through the 

 mass to the same depth. Eastward the top of the terrace rises 

 gradually past the contour of 1560 metres, and then steeply up to 

 Clavadel. This village is also situated on the comparatively level 

 top of a mass of superficial deposits : the rock in situ being exposed 

 many metres above. Looking up the Sertig Thai, the remains of a 

 former extension of the same deposits may be seen far higher up the 

 valley. There is a large mass left on the southern side, behind the 

 electrical works at Bei der Sage ; and a chalet at Stadel stands on 

 a similar terrace, at a height of nearly 1800 metres. 



The flat top of the Wildboden and Junkersboden terraces has 

 naturally suggested to some the idea of deposition in a lake ; but 

 there is no doubt that the whole series form part of a great detritus- 

 fan which at one time filled the Sertig Yalley, and was banked up 

 against the mountain-slopes west of the Landwasser. Enormous 

 as the amount of transported material is, once it was much greater, 

 as the height of the remains on the side of the Sertig Yalley con- 

 clusively shows. Clavadel itself stands 100 feet higher than 

 Wolfgang, and the maximum height of the detrital mass must have 

 been considerably above that. 



Such a barrier as this would have been quite sufiicient to hold up 

 the waters of a lake reaching north to the Wolfgang-Drusatch ridge. 

 That the cutting-through of its margin by the Landwasser is of 

 relatively late date is shown by the sharp angle made by its terminal 

 bank with the surface- contour. 



Further evidence is now obtainable, owing to the fact that a 

 cutting is being made on the west side of the Landwasser opposite 

 Wildboden. Here is a large rounded mound projecting towards 

 the river. While intact, this would have been naturally regarded 

 as part of the talus from the western mountains. Its excavation, 

 however, proves it to be a part of the great Sertig fan cut off from 

 the main mass by the recent erosion of the Landwasser. The 

 beds of sand and pebbles of which it consists dip at an angle of 

 some 30° to the north and west ; and this high angle confirms the 

 impression of the great vertical height of the ancient barrier. 



So far, then, as a general observation of the valley is concerned, 

 one is led to the following conclusions : — That throughout the whole 

 area the river is running over superficial deposits, and its course gives 

 no indication of the real contour of the rock-bed; that the lateral 

 talus-fans have been cut through at a relatively recent date since 

 their accumulation ; that the northern end is blocked by moraine- 



