part 1] ANNIVERSARY ADDRESS OF THE PRESIDENT. lxxvii 



water in addition to its own local precipitation : the latter at that 

 time probably all pent up as snow during the winter, and released 

 suddenly in the spring to augment the Hoods from the ice-sheet. 

 Therefore it is not surprising that the glaciation-features of such 

 areas have acquired a more mature and subdued aspect than the 

 corresponding features of the country sloping to the sea-basins, 

 uncovered later and never inundated in the same wa3 r by thaw- 

 water. But I do not think that this difference of aspect in the 

 case of the English drifts implies more than a comparatively un- 

 important difference in time, or that there is room or evidence for 

 an interglacial period, as is sometimes supposed, between the 

 inner and the outer drifts. 



The Hill-Drifts. 



There remains to be considered the effect of the glaciation upon 

 the hills. As I have mentioned alreacby, this effect has been com- 

 paratively slight so far as the main features are concerned ; never- 

 theless, in the detail almost everywhere much new shaping has been 

 done, and the old shapes modified. The work of Prof. P. F. Kendall 

 in the Cleveland Hills some years ago called attention to the 

 peculiar and characteristic erosion-forms produced by the damming 

 and diversion of the drainage in country just outside the margin of 

 the ice-sheet; and many observers have since found that similar 

 phenomena are recognizable in the hill-regions all over England and 

 Wales, as well as in Scotland and Ireland, wherever ice-sheets or 

 glaciers have blocked the pre-existing slopes and channels of dis- 

 charge. These new features are particularly prevalent on the outer 

 slopes of the hill-masses ; and they generally indicate that the high 

 ground, if ever covered, became free from ice long before the plains 

 were uncovered. The 'overflow channels,' ' dry gaps,' ' delta-fans,' 

 'corroms,' and other phenomena due to these conditions have, at 

 this day, been so frequently described that I need but mention them 

 to recall how material in the aggregate is their influence on our hill- 

 scenery, of which they not rarefy provide the most picturesque 

 incidents. 



These effects we may regard as interlinked with, and dependent 

 upon, the glaciation of the lowlands. But to the hills more 

 peculiarly belongs another group of phenomena, so conspicuous in 

 aspect and so convincing as to origin, that it was the first to secure 

 attention in the early days of our science, and to obtain recognition 

 as proof of the existence of ancient glaciers in Britain. I refer, 



