572 TRANSACTIONS OF SECTION C. 



support the view that mild interglacial conditions obtained at any time in that 

 region between the deposition of the Cromer Till and the ' cannon-shot ' gravels 

 which overlie the chalky boulder-clay. 



7. Lake Oxford and the Goring Gap. By F. W. Harmer. 



Deep borings at Sandy, Newport, and Hitchin, and further west at Stony 

 Stratford, reveal the existence of drift-filled valleys, extending in one case to a 

 depth of 140 feet below sea-level, which were probably connected with that of a 

 pre-glacial river running in a north-easterly direction towards the North Sea. 

 Similar deep borings at Boston, Fossdyke, and Long Sutton may represent the 

 mouth or the seaward extension of such a valley. 



As far as the Midland Counties are concerned, the gorge at Goring is unique. 

 At no point between Newmarket, in Suffolk, and Blandford, in Dorset, in the one 

 case, or between Lincoln and Brad ford-on- A von on the other, have the Cre- 

 taceous or Oolitic ranges been cut down to the base level of the plains, or does 

 water run through them from one side to the other. Cases similar to that of 

 Goring occur, however, at three of the places named, as well as at Ancaster, and 

 at Ironbridge, in Shropshire. All these are of a distinct type from the dip-slope 

 valleys of the Oolitic and Cretaceous ridges, and they must have originated in a 

 different manner. They have certain striking features in common. Not only do 

 they cut continuously through the ridges, at right angles to the natural drainage 

 of the plains, but they form narrow, sharply cut, U-shaped gorges, having an 

 extremely modern appearance, as distinguished from the older-looking, wider, and 

 more gradually shelving basins of the dip-slope rivers. They are invariably 

 accompanied by lake-like depressions, lower than the general level of the plains, 

 opening into trumpet-mouthed gorges, through which the former are drained. 



Dealing first with the gorges at Lincoln and Ancaster, the effect of the advance 

 of the Vale of York glacier to Barnsley and Doncaster, and the obstruction of the 

 gap separating the Yorkshire from the Lincolnshire Wolds by the North Sea ice, 

 as explained in a former paper, must have impounded the drainage of the Trent 

 basin and caused the formation of a lake, the overflow of which could only have 

 escaped over some part of the Lincoln ridge. Unless the Lincoln and Ancaster 

 gaps were already in existence, which seems to the author improbable, some such 

 overflow must have been initiated at that time. The continuous advance of the 

 Trent glacier southwards would eventually have blocked the Lincoln gorge, 

 probably with drift, and the Ancaster gap would have been originated, being 

 afterwards similarly blocked, in its turn, as the ice moved on. These channels, 

 however, would have been reopened successively, and probably deepened, when 

 the ice retreated. 



Referring next to the case at Goring, we find scattered over the low country 

 round Oxford a number of isolated hills, generally capped by gravel, the origin of 

 which it is not easy to explain on the hypothesis of the fluviatile erosion of the 

 Oxford plain ; they present no such difficulty, however, if we regard the latter as 

 the site of an ancient lake, the bottom of which has been gradually lowered. 



It has been long known that the gravels in question contain Triassic pebbles, 

 but it is still more important to notice the presence in them, often in great abun- 

 dance, especially as they are traced towards the gap, of grey Lincolnshire flint. 



This flint drift connects itself with a great trail of such detritus extending con- 

 tinuously from Buckinghamshire to the AVolds, being exceedingly common both in 

 the chalky boulder-clay of the Ouse basin and in the gravels into which the latter 

 passes towards the south-west. 



The grey flints occur in the highest part of the Oxford gravels, at elevations 

 exceeding 400 feet, as, for example, on a hill immediately to the south-west of that 

 place, and at Basildon, near Goring, above the narrowest part of the gorge. The 

 erosion of the Oxford plain, and of its outlet below that level, cannot, therefore, 

 have commenced until after the arrival of the glacial drift in that region. 



Other gravels, also containing Triassic pebbles and Lincolnshire flint, occur at 



