288 iiE. A. VAFGaAjr jennin-gs on [Aug. 1S98, 



weathering through an enormous period of time, but no erratic 

 blocks of it occur along the lake-side, nor indeed anj^where south of 

 the lake -head. This fact alone seems to me to be conclusive as to 

 the former direction of drainage ; but there is also positive evidence 

 in the presence, north of the lake, of many rocks that can have come 

 only from the south. 



In the Fluela Pass one of the most conspicuous rocks is a coarse- 

 grained white augen-gneiss derived, I believe, from the region of 

 the Weisshorn. Erratic blocks of this occur frequently near the 

 foot of the pass, along the lower slopes of the Seehorn, and on the 

 Drusatch Alp. 



Blocks of a muscovite- granite are abundant behind Hohwald, at 

 the head of the lake, and appear to be erratics from the mass 

 which crosses from the Schaflager to the Mittelgrat. 



Another important constituent of the moraine is the dark compact 

 hornblende-schist with veins of epidote, which occurs in situ on the 

 Dorfliberg and elsewhere south and east. A group of huge erratics 

 of this rock, one of which must contain some 2000 cubic feet, may 

 be seen at the north-western corner of the lake. 



More important is the common occurrence between Hohwald and 

 Wolfgang of limestone-fragments. The present river-system could 

 not bring them to this point either from the "Weissfluh or Casanna; 

 they must have travelled from the limestone-mass above Davos. 



The same is the case with the verrucano. Fragments of this 

 are common in the moraine from "Wolfgang to Laret, but the rock 

 does not occur in the region above. They must have come also 

 from the south, and most probably from some point above Frauen- 

 kirch. 



All observations of transported blocks thus tend to show the 

 northward movement of the ice, while there is a striking absence of 

 any proof of the reverse condition. 



Such being the characters of the area, it only remains to attempt 

 a reconstruction of its more recent geological history. 



The general direction of the Fluela, Dischma, and Sertig valleys 

 points to the conclusion that they formerly discharged their waters 

 northward into the Landquart basin ; and the evidence of former 

 ice-movement is entirely in favour of this view. The watershed 

 was then apparently between Davos and Frauenkirch, perhaps 

 nearer the last-named locality. 



During the glacial time the ice-borne blocks from these valleys 

 and from the Todtalp were accumulating. When climatic con- 

 ditions became less severe and the ice receded, the resulting moraine 

 held up the waters of the lateral valleys and caused the lake, which 

 probably extended to Frauenkirch and was there banked up by the 

 great detritai fan of the Sertigthal. When running water became 

 once more the chief agent of change, the relatively small streams at 

 the northern end could have but little effect in removing the solid 



