488 J. O. Ooodchild — On the Origin of Coums. 



they occur in rocks of tolerably uniform lithological character 

 throughout great thicknesses of strata, there does not seem to be 

 much difficulty in accepting the theory that attributes their origin 

 to the combined action of springs and meteoric agencies. But 

 where, as in the Lower Carboniferous rocks of the north-west 

 of England, we find them just as perfect in form in a series of 

 rapid alternations of horizontal strata that have very different rates 

 of destructibility under any kind of disintegrating influence, many 

 difficulties arise which plainly show that this theory is untenable. 

 In the paper referred to at the head of this communication it has 

 been shown that, under purely subaerial influences, the form of 

 the surface that would be developed out of any such series of rocks 

 as those in the Dale District would be in many respects different 

 from what we actually find. 



Just to take one objection — all the springs in the Dale District 

 tend more or less to break out along certain definite lines, most 

 frequently between a limestone and the less pervious grit or sand- 

 stone that it lies iqoon. Hence, the tendency of springs, as they 

 act rather by undermining than by actual erosion, would be in 

 nearly all cases to cut back the beds above that whereby the spring 

 is thrown out. As a result, the lower bed would soon be left as 

 a shelf projecting beyond the outcrop of the next bed above ; 

 unless there happen to be springs below which undermine the 

 impervious bed at the same rate as that maintained by the higher 

 springs. Even in that case the result would soon take the form 

 of a gully or ravine, in no way different from an ordinary bed 

 of a stream; and it is obvious that unless springs were acting 

 simultaneously over the whole surface — or, what amounts to the 

 same thing, unless the springs are continually changing their point 

 of outburst so that the whole rock surface is uniformly acted 

 upon — the result must inevitably present a jagged and irregular 

 contour at all elevations ; which is a form of surface totally unlike 

 almost any unmodified part of a single coum that I have ever seen. 

 Again, the objections brought forward against the subaerial origin 

 of the straight lines of scar in the Dale District apply equally 

 well in these cases ; because it frequently happens that the more 

 prominent rock features in the coums consist of the kinds of rock 

 that, under subaerial influences, tend to disappear with the greatest 

 rapidity, while, at the same time, they are the rocks that are best 

 capable of withstanding erosion by mechanical means. Besides 

 these objections there are others that are set forth in the paper 

 on Glacial Erosion. But even if these objections did not suffice 

 to show the untenability of the Spring Theory, the existence of such 

 one-sided pot-hole-like hollows in rocks of very different litho- 

 logical character and lying at every imaginable angle seems to shake 

 one's faith in any of the theories that have yet been proposed to 

 account for their origin. In the case alluded to, which is along 

 the Cross Fell Escarpment between Melmerby and Ousby, in 

 Cumberland, the rocks forming the coum consist of highly inclined 

 and contorted Lower Silurian ; thick masses of vertical and highly 



