SOME VEGETATION TYPES AT HIGH ALTITUDES. 47 



aspen {Fopuliis treinula), and rowan (Sorbus auciiparia) 

 were observed. 



The localities in which observations were made include 

 practically the whole of Val Cluoza and Valletta, Piz Quater 

 Vals and Piz Murter, part of the SpOltal, and the watershed 

 between Val dell Acqua and Val della Fuglia. The total area 

 has an altitudinal range of nearly 5532 feet, from 4832 feet at 

 Zernez to 10,364 feet at Piz Quater Vals, the limit of tree 

 vegetation being about 7700 feet. The configuration of the 

 land is varied, and consists essentially of acute ridges extending 

 to the snowline, the upper slopes of which are, for the most 

 part, covered with loose frost-debris. In other parts these 

 ridges constitute upland meadows. On the middle valley-slopes 

 coarse gravel screes predominate, and these pass into block 

 screes at lower levels. The valley bottoms are narrow and 

 contain morainic material, while in the side valleys small 

 glaciers occur. 



The main physical features of the area are the two large 

 valleys, Val Cluoza and Spoltal, which run parallel for some 

 distance and join east of Zernez. These communicate with 

 numerous side valleys which are usually short and steep. 

 The rocks of the district consist of Dolomite and Muschelkalk 

 beds resting on a floor of gneissic material. In places, for 

 example at Cliiz-Zernez, the underlying gneissic base is 

 exposed and is there seen to consist of Augengneiss. 



Step-For MATiON ( Treppcnbildung), 



In the area under consideration this formation is found at 

 the limit of forest growth, and in fact of all other closed plant 

 associations. At a higher elevation occurs the zone of alpine 

 cushion-plants including Androsace helvetica, Siletie acaulis, 

 Eritrichium nanu/n, etc. Papaver alpinum also occurs here, 

 together with a few species of lichen. The above plants, 

 however, have quite a sporadic distribution, and cannot be said 

 to form any definite association. Step-formation characterises 

 the higher slopes of fine frost-debris, as also the wash-out 

 channels, although in these it descends to a lower level. This 

 would seem to indicate that while a certain stability of soil 

 is necessary for the individuals which produce the steps, the 

 formation is the pioneer on slopes lying at the angle of repose. 

 Soil-creep combined with wind action tends to make the 



