J. R. Dakyns — Sediment Theory of Drift. 169 



To my mind one of the great difficulties connected with the Drift 

 has always been to account for the uniform distribution of Till 

 along the bottom and flanks of valleys. A terminal moraine 

 thrown down at the stationary end of a glacier, or lateral moraines 

 similarly dropped along the flanks of the melting ice, or a heap of 

 bottom or ground moraine shoved forward by the snout of an 

 advancing glacier or the edge of an advancing ice-sheet, and there 

 left on the retreat of the ice, or deposited in sheltered spots under 

 the lee of hills or bosses of rock, — these phenomena were intelligible : 

 but how a uniform sheet of Till should be left along a smooth 

 valley or on open ground was not intelligible on any land-ice 

 theory. Geologists but conjured with the term " moraine profonde." 

 The ice that scored and polished the solid rock could not at the 

 same time be moving over a cushion of Boulder-clay. It must have 

 been in contact with the rock : it might accumulate the waste of 

 the polished rocks as Till in isolated sheltered spots ; but not uni- 

 formly over the face of the country, and least of all where the 

 underlying rock shows signs of glaciation ; in fact, the mere exist- 

 ence of Till itself negatived the idea. Yet such was the manner of 

 Drift distribution. Anxiously I have scanned the edges of the 

 Norwegian ice-fields for a solution of the difficulty, but in vain. 

 Mr. Goodchild's theory of the deposition of the Till, as a sediment 

 melted out of the ice in place, seems to me to remove all difficulty 

 on the subject. But the difficulty of understanding how the ice 

 got the stones with which it was charged, where the country was 

 so buried in ice that no rocks remained sticking out to afford 

 detritus by their waste under frost, remains the same. I have 

 myself suggested 1 an explanation; but at first sight there seems 

 to be a contradiction between the smoothed surfaces of ice-worn 

 rocks, so difficult for the weather to take hold of, and the idea of 

 frost disintegration sub-glacially. 



Some phenomena, too, of Drift distribution cannot be explained 

 on the Sediment theory. Such a theory will not account for the 

 presence of Drift on one side of a valley rather than on the other, 

 nor for the accumulations of Drift specially in the angle between two 

 valleys at their junction. These phenomena, on the other hand, 

 can be fairly accounted for on the supposition of the Drift material 

 having been dropped by the moving ice, and left in sheltered places. 



While, however, the sediment theory accounts very well for the 

 uniform spread of Till, I cannot understand how well- washed current- 

 bedded sands and gravels are to be explained on this theory. Nay 

 more, even granting that they may be so explained in some cases, 

 there is still no explanation of such a general phenomenon as the order 

 of the Lancashire Drift, consisting of two beds of Till, with an inter- 

 mediate set of washed sands. "Why should the sediment melted out 

 of the ice occur in this fixed order ? Such a sequence bespeaks a 

 sequence of conditions in time. On the Sediment theory there should 

 be no other arrangement than a horizontal one, whereby the sedi- 

 ment should be found to be more rounded, and with more frequent 

 1 Geological Magaziine, Vol. X. No. 2, February, 1873. 



