J. G. Goodchild — On the Origin of Coums. 487 



In all such instances that have hitherto come under my notice, both 

 in the Dale District and elsewhere, there are certain points of resem- 

 blance common to all. In their lower parts, many, perhaps nearly 

 all, hardly differ in any noticeable respect from the steeply sloping 

 head of an ordinary valley, except that they are, perhaps, of some- 

 what greater width. The bottom of the hollow is almost invariably 

 occupied by a stream, of which a part is often so much enlarged 

 as to form a tarn, and in a few cases the tarn can be shown to lie in 

 a true rock basin. Looking upwards at the higher parts of the 

 coum from the position of the tarn, one cannot fail to be struck with 

 the sweeping outline of the walls of the amphitheatre as these are 

 seen against the sky. In many instances the curve is so regular, and 

 so little interrupted by stream courses, that it seems rather as if the 

 shape had been produced by artificial means than by purely natural 

 causes. Viewed from the sides, at a higher elevation, the regularity 

 of the curvature is quite as obvious. From such a point, too, one 

 can see how markedly the valley-like form of the amphitheatre's 

 lower part contrasts with the sweeping curves of the parts nearer 

 the top, and how gradually the contours change in form from one ex- 

 treme to the other. Above the line where the greatest regularity of 

 form is observable the coum frequently terminates somewhat abruptly 

 among rock features that do not present any striking or unusual 

 peculiarities. In nearly all cases it is abundantly manifest about all 

 such amphitheatric recesses that they are slowly, but surely, losing 

 their regularity of form and smoothness of outline. "Wherever a 

 spring bursts forth, the continuity of the curves is more or less in- 

 terrupted, and the slopes below are encumbered with the rock that 

 has been thus undermined ; and the gully formed by any stream that 

 flows downwards from the edge of the coum is quite unlike any part 

 of the smooth, concave surface of the other parts. That very little 

 denudation has taken place in Post-Grlacial times in these cauldron- 

 like hollows is evidenced by the presence, high up on the sides of 

 the hollows, of glacial drift that in a few cases can be shown to date 

 from the last ice-sheet period ; moreover, glacial stria? are found in 

 a few instances in such a position and with such directions that it is 

 plainly impossible that the form of the surface can have undergone 

 any important modification since it was left by the great ice-sheet — 

 a view that is further borne out by the general freedom of the drift 

 surface from fallen rock fragments from above. Indeed, in a few 

 instances it would seem as if so much of the old weathered part of 

 the rock was removed by the ice-sheet that subaerial forces have 

 only just begun to produce any noticeable effect upon the sweeping 

 outlines of the surface. It may be true that in the case of many 

 coums these remarks do not apply ; but if they can be shown to be 

 true of one only, it proves that in that particular instance the pecu- 

 liarities of surface configuration have been produced by other 

 agencies than those now at work upon the surface. 



Several theories have, at different times, been advanced to account 

 for the origin of these singular crater- shaped hollows ; but hitherto 

 no thoroughly satisfactory explanation has been given. Where 



