Vol. 63.] ORIGIN OP CERTAIN CANOX-LtKK VALLEYS. 511 



PI. XXXV illustrates the profile of the country and of the 

 dip-slope streams from the crest of the Jurassic escarpment to 

 the Thames Valley, starting from two points, one on the east of 

 the Cherwell, and the other on the west. Both sections cross the 

 . Oxford plain, the first following the Vale of Aylesbury, the other 

 intersecting one of the Corallian hills east of Oxford. The 

 Gherwell takes its rise on a wind-gap about 200 feet below the 

 summit of the escarpment, from which also a small obsequent 

 rivulet finds its way northwards to the Avon. 1 



Another section, from the basin of the Avon to that of the 

 Thames, shows the Moreton watershed and the profiles of the 

 valleys which descend from it. That of the Stour, a pre-Grlacial 

 and obsequent stream of the Cotteswold region, closely resembles 

 the Hitchin valley in the Chalk-range (see map, PI. XXXIV), 

 while its neighbour, the Evenlode, corresponds to the Lea and its 

 affluents. In each case the gradient of the consequent streams is 

 conformable to that of the dip-slopes. 



Applying Prof. Davis's hypothesis to the region traversed by 

 these sections, however, let it be conceded, for the sake of argument, 

 that a river may have once flowed from some point above the 

 present summit of the Cotteswolds to the Chilterns. On that 

 view, the two escarpments with the dip-slopes and the inter- 

 vening lowland were carved, at some subsequent period, out of the 

 peneplain, the distribution of the Glacial Drift indicating that this 

 took place in pre-Glacial times : the profiles of the dip-slopes, 

 however, have no obvious relation one to the other, or to what 

 may have been the gradient of the suggested peneplain. 



On the contrary, the dip-slope valleys, conformable to the ex- 

 isting contours, were eroded after the surface of the land had 

 assumed its present form : their erosion having been separated 

 from the penepla n-stage by a considerable and unbridged interval. 



The more important rivers of Central England are longitudinal, 

 following the strike of the Triassic and softer Jurassic rocks, along 

 which the predominant erosion has taken place, the transverse 

 drainage being subsidiary to that of the plains. 



1 It may be said ' t, on the view taken in this paper, the Cherwell should 

 have turned sout 1 twards before joining its main river, as do the other 

 Cotteswold stream .hereas at present it points southwards to Oxford and 

 Goring. The lowe part of its valley has been eroded, however, since the 

 drainage began to fl v through Goring Gap, having been cut down to its 

 existing level (betwee: 200 and 300 feet above sea-level) pari passu with the 

 excavation of the gor^ The present course of the Lower Cherwell, therefore, 

 does not necessarily h icate that of pre-Glacial times. The pre-Glacial Cher- 

 well, however, may 1 ~e turned to the south-east, as, for example, in the 

 neighbourhood of Hai^wick, flowing over the comparatively low ground of 

 that district to the primeval Isis through some channel, now obscured by the 

 Drift which the map of the Geological Survey shows to extend continuously 

 from Buckingham to a point near that village, not far from the Cherwell 

 Valley. It should be stated, moreover, that it was by the Evenlode route, 

 rather than by that of the Cherwell, that the Triassic Drift was carried to 

 Oxford and Goring. 



Q. J.G.S. No. 252. 2o 



