126 MR. A. MOXTGOMERIE BELL ON [^ av I 9°4) 



I replied that I had not : that I had examined the exposed parts, 

 but found nothing. He remarked that it was unlikely that I should 

 find them. 



This previous surface has now proved to be implementiferous ; 

 there are side by side two implement-bearing deposits, different in 

 character and different in age. 



This surface consists of a series of troughs formed in the clay, 

 and rilled with gravel, sand, and earth. The stones which the 

 troughs contain consist largely of quartzites, lydian-stone. and 

 quartz-pebbles. These pebbles all belong to the ' Xorthern Drift,* 

 by which name Prof. Green told me to style the deposit. In this 

 Prof. Phillips would, I imagine, have agreed with him. In the 

 * Geology of Oxford & the Valley of the Thames* (1871) pp. 457-58, 

 Phillips wrote : — 



• To these I assign the title of Hill-deposits, not that they are exclusively 

 found on elevated ground, but because this fact is characteristic of them, in 

 contrast with the others. Scattered materials of these hill-gravels are often 

 found in low ground mixed with those in the true valley-deposits, under 

 circumstances which indicate the anterior date of the former.' 



This exposure was not expressly mentioned by Phillips, although 

 it was in his time exposed in a railway-cutting, which adjoins 

 the section now under discussion. At the same time, besides 

 the northern pebbles, we also find in the troughs much g ravel 

 from the Thames Valley, limestone-pebbles, and Oolitic fossils, 

 together with sand. The presence of these materials has led me to 

 regard the Drift as not the true Northern Drift, which caps the 

 hills around at a level of about 500 feet, while the Wolvercote level 

 is 240 feet, but as a Thames-Valley Ice-Drift, consisting largely of 

 a remaniment of the Xorthern Drift. 



The AVolvercote Drift shows itself in somewhat flask-shaped holes 

 in the clay, filled up by gravel, and with columns of clay between, 

 still attached to the unbroken Oxford Clay beneath. The question 

 arises as to how such a drift is formed. Is it a drift of rain wash ? ; 

 or is it perchance no drift at all, but the result of underground water 

 forming holes in the clay, which are filled up by the infall of surface- 

 stones ? ; or, again, is it an ice-drift ? It is not a rainwash-drift, 

 because, if it were, it would not have narrow inlets at the top, which 

 spread out beneath, but would be spread out over the surface, with 

 slight traces of bedding. Xor has it been caused by underground 

 water, as the action of water would be visible at the lowest point 

 where the flow was continuous ; the stones at the sides would 

 also have a tendency to drop towards the centre, when the stream 

 was carrying away material. There are no traces which lead me 

 to attribute it to this cause. 



It is otherwise when the ice-drift hypothesis is tried ; for here 

 there are several salient facts which find an explanation. The 

 troughs are fan-shaped. The pebbles in the centre have their 

 longer axes pointing downward, while at the sides they are 

 horizontal. This seems to show that they were pressed down 

 by a weight above them, which, as it forced them to move into the 



