23i> 



MR ALFRED HARKER ON 



2050 



the characteristic canal-shaped or ' U-shaped ' cross-section (figs. 2 and 5) recognised 

 in many other glaciated areas. The persistence of this form of cross-section along the 



middle and principal part of the valley's 

 course, in conjunction with the straight - 

 ness and smoothness of the sides, 

 already adverted to, results in some- 

 thing like a semi-cylindrical shape in 

 this portion of the valley, when most 

 typically developed. Since it is 

 difficult to visualise the actual shape 

 of a valley from a contoured map 

 alone, a rough attempt is made in 

 figs. 3 and 4 to render it in another 

 fashion. The appearance as seen on 

 the ground is quite marked. One may 

 describe it roughly by saying that the valleys give the impression of trenching unduly 

 upon the dividing ridges and being too large, and in particular too wide, for the district. 



S.W. 



N.E. 



Fig. 2. — Transverse section of the Coruisk valley about ^ mile 

 above the head of the loch ; scale, about 2J inches to a mile. 

 The horizontal line shows the sea-level (O.D. ). 



This and the other sections are drawn from the contoured 

 Ordnance Map with the aid of additional altitudes taken 

 with the aneroid. They are drawn to true scale as regards 

 horizontal and vertical distances, but they cannot pretend to 

 close accuracy in detail. [The original drawings have unfor- 

 tunately been reduced on no settled scale.] 



Fig. 3. — Ground Plan of Coir' a' Ghrunnda. 



Fig. 4. — Ground Plan of Coire Labain. 



The lines in these two figures are not contour-lines of the ordinary kind. They are intended to show elevations, not 

 above sea-level, but above the neighbouring floor of the valley ; thus eliminating the inclination of the valley-floor itself. 

 The figures bring out well the form of the cirque in which any of these valleys heads, as described below. Of the two, 

 Coir' a' Ghrunnda has a very elevated cirque and a semicylindrical middle course ; Coire Labain has a larger cirque at a 

 somewhat lower level, and a rather more open valley below. Scale, about 3 inches to a mile. 



It remains to consider the tributary glens in their relation to the trunk valley to 

 which they belong. In so far as the ice filling the latter moves as a solid body, it must 

 tend to pond back the smaller tributary ice-streams, at least when these debouch in 

 directions making high angles with the trend of the main valley. We must expect 



