72 J. G. GOODCHILD ON THE GLACIAL PHENOMENA OF THE 



flows was not initiated by glacial action, although its direction so 

 nearly coincides with that of the flow of the ice there ; for we find 

 patches of Permian rocks in the very bottom of the valley, proving 

 beyond all doubt that a ravine existed there in pre-Permian times. 



It may well be doubted whether many instances of considerable 

 valleys which have clearly originated by glacial action can be 

 pointed out, as it is nearly always difficult, if not impossible, to 

 prove that they are wholly the work of ice. The evidence seems 

 rather to prove that the ice ground down most of the minor ine- 

 qualities of the surface, and thereby tended to efface the preglacial 

 channels of the lesser streams, and that, where the pressure and 

 rate of flow of the ice were nearly uniform over large areas, it 

 tended to level these into plains instead of ploughing out great 

 parallel furrows in them. 



In those parts of the Dale -district valleys where the lower strata 

 of the ice can be shown to have flowed nearly along the windings 

 of the dale, the alternations of hard and soft beds that make up 

 the dale-rocks have given rise to more striking terraces than are to 

 be found in other parts where the ice is known to have crossed the 

 lines of outcrop at a greater or lesser angle. Where the direction 

 taken by the ice has nearly or quite formed a right angle with the 

 line of outcrop, we generally find that the characteristic surface- 

 features of the dale-rocks are entirely wanting; and even where 

 there are thick beds of limestone, the long lines of swallow-holes 

 that almost everywhere else accompany beds of limestone in the 

 dales, are generally absent. In the terraced parts of the dales, no 

 matter what may be the width of the terrace, the swallow-holes, 

 save an occasional one here and there, are only to be found along 

 the line where the usually soft overlying beds come on. In no 

 instance yet known to the writer do these swallow-holes extend far 

 from the inner margin of the terrace towards the scar at its outer 

 edge. In addition to this it is unusual to find the limestone of the 

 lower terraces much more weathered, or wider joint-fissures deve- 

 loped in it nearer the scar-margin, than may be found all over its 

 surface up to the swallow-holes. 



In considering the causes that may have helped to shape these 

 terraces, we may leave marine action entirely out of the question, 

 because they are confined to particular beds of rock, and go with 

 them through all their variations of dip and elevation. Streams 

 rarely run along the foot of the scar or along the inner margin 

 of the terrace ; and those that do so are so small that they cannot 

 remove any appreciable quantity of weathered debris from the rock 

 above. Springs can do little else than undermine the part of the 

 scar from which they issue, and in that way cut it back into a 

 notch ; the greater the number of springs issuing from the base of a 

 scar, the more is it notched and changed in outline. 



Landslips can effect but very little. It is true that great masses 

 of rock are frequently removed from the scars in this way ; but the 

 crescent-shaped hollows that are left, and the great heaps of fallen 

 material remaining at the foot of the scar, are very different from 



