U 
Exposure, while paramount in importance, is not the 
only factor to be considered. The nature of the soil plays a 
part, and is of particular importance when the slopes are 
covered by talus, — masses of great stones or boulders hurled 
down the mountain-side, — for these cover the surface of the 
ground and protect is against the rays of the sun, and it is 
safe to surmise that much moisture is to be found beneath 
them. The unusual vegetation characteristic of such places 
indicates the same. (More of this matter below page 93.) 
The talus of small stones or gravel, which I have seen in a 
few places, were either nearly or totally barren, probably be- 
cause the bottom is constantly changing: the continual great 
variations in temperature bring about a rapid denudation, 
followed by a constant supply of new gravel and small stones 
rolled down from above. On account of the fineness of the 
material the masses are easily set in motion. In Switzerland 
such localities have their “Schluttpflanzen”, as we know from 
SCHRÖTER and others. 
The importance of exposures may be seen at a distance. 
On account of the vegetation the bottom of the dry stream 
clefts appear like dark lines (see fig. 7) on the moun- 
tain-sides. On looking more closely, but still a good way 
off, we see that on a slope with an eastern or western ex- 
posure, the dark line of vegetation lies south of the bottom 
of the cleft and along the southern shore of the bed of the 
stream; i. e. on the side with a northern exposure, — and, 
on approaching more closely, we find that not only the bottom 
of the cleft but the slopes as well have a different vegetation 
on the north and south side; everywhere the localities with 
a northern exposure have more luxuriant plant growth, than 
those exposed to the south. A few examples illustrating this 
are given below. 
Going north on the Mardjanaj-plain, described earlier, 
along the Mardjanaj River, one finds many larger and smaller 
clefts cut by small streams now dry, and leading into the 
river; their main direction is east-west. 
The slope toward the north of one of these, was closely 
grown with Artemisia sp., Solenanthus stylosus, Trigonella Emodi, 
Carex stenophylla, Oryzopsis molinioides, as well as a few spe- 
