232 F. R. Cowper Reed — Carries of Gomeragh Mountains. 



suitable. Major lines of weakness, sucli as faults, will also be 

 favourable for the development of cliffs. 



It is probable also that in the first instance some suitable 

 configuration of the ground at the head of the glen must have 

 -existed, such as the presence of a bare rock-face, more or less 

 vertical, which may have been caused by a landslip due to the 

 bursting out of springs at or near the base of a steep terminal slope. 

 A cliff under the above-mentioned conditions would tend to be 

 preserved, and by eating its way backwards into the slope would 

 increase in height and extent under the action of weathering, 

 particularly of frost, as is the case in Norway. The aspect of such 

 a cliff with respect to the four quarters of the compass would have 

 also some effect in determining its preservation and growth ; and 

 the fact that the majority of corries face north or north-east, 

 and are rare on the other slopes of mountains and on escarp- 

 ments facing in other directions, has been noticed throughout 

 Europe.' Their position has sheltered them from the moisture-laden 

 winds from the south-west and from the consequent rapid denudation 

 vphich takes place under their influence. If ice and snow have, 

 moreover, played a considerable part in the development of the 

 peculiar characters of conies, it is on the northern sides of mountains 

 that ice and snow would linger longest. 



If we regard cirques to be of the nature of valley-heads formed 

 under special conditions we have not even then surmounted all the 

 difficulties connected with them. For we still have to explain their 

 shortness in proportion to their width, their flat or excavated floors, 

 their U-shaped cross-section, their frequent horse-shoe shape, and 

 their occurrence as niches or recesses high upon the lateral flanks of 

 main valleys or on escarpments, with their floors nearly level or 

 even hollowed out, and the ground from their mouths sloping down 

 steeply to the base of the mountain-side. The problem is of the 

 same essential character as that of ' hanging valleys,' and some 

 geologists regard them as merely hanging valleys of a special type 

 and with a special history. Their niche-like position has been 

 accounted for by supposing the main valley to have been widened 

 and over-deepened by ice or water, while erosion in the lateral 

 valleys was checked. It has been contended by Professor Davis 

 that the glacier of the main valley has ground out its channel, 

 deepening it and widening it at the expense of the lower parts of 

 the lateral valley, which were occupied by small glaciers joining 

 the main glacier at the level to which its mass rose against the 

 lateral slopes. The main ice-stream in this way passed transversely 

 across the lower ends of these tributary valleys, planing them 

 down and truncating them abruptly. The corries in Skye have 

 been thus explained,- and the hanging valleys of the Rhone. But 

 this theory meets with much opposition. In the case of the Alps 

 a general post-glacial or inter-glacial uplift has been suggested, 

 when the main valleys would tend to be rapidly excavated by 



' Penck: Morphol. d. Erdoberfl., ii (1S94), p. 310. 



2 Harker: Trans. Koy. Soc. Edinb., vol. xl, pt. 2 (1901), pp. 221-252. 



