556 Geological Society. 



caused by outflow from a Church-Stoke lake which was driven 

 into the Ordovician ground to the north and east. Lake Trow- 

 bridge and the gorges of Clifton aud Bradford-on-Avon are next 

 dealt with, the latter being attributed to the overflow of a Glacial 

 lake occupying the Trowbridge plain, and the former to the blocking 

 of the Elax-Bourton valley by ice. The gaps in the Jurassic escarp- 

 ment at Lincoln and Ancaster are explained as overflows from a lake 

 caused by the damming of the Trent outlet towards the Humber. 

 This gave rise at first to the more northern, and later to the 

 southern gorge. Finally, Lake Oxford and the Goring Gap are 

 dealt with in considerable detail. Certain Drift-filled valleys are 

 regarded as excavated by a river flowing from the south-west — the 

 primaeval Thames. The distribution of the Chalky Boulder-Clay 

 shows that the advance of the Great Eastern Glacier from the north- 

 east must have arrested drainage flowing towards the Wash, and 

 caused a lake which may possibly have first overflowed through the 

 Newport valley into that of the Stort, or by the Hitchin valley into 

 the Lea, or later into the Colne by the Leighton-Buzzard valley. 

 "When the ice reached Buckingham, such channels were closed and 

 the overflow must have taken place farther to the south-west, over 

 what are now the Tring, Wendover, and Wycombe Gaps, and 

 eventually by the Goring Gap itself. 



Gravels containing Triassic and drifted flint-pebbles derived from 

 Glacial deposits maybe traced from Goring across the Oxford Plain, 

 at an elevation of between 400 and 500 feet, into the Evenlode 

 Valley, and thence into the basin of the Avon. Their occurrence 

 on the higher slopes of the Goring canon indicate that the excava- 

 tion of the latter did not commence until after the arrival of 

 glacially-derived detritus in the region in question ; the Goring Gap 

 is, therefore, of Glacial age. 



The author is unable to reconcile the views here given with 

 those of Prof. W. M. Davis on the valley-erosion of Central England. 

 Any relation which may have existed between the present drainage- 

 system and that of some former period when a peneplain may have 

 extended over the Jurassic and Cretaceous formations alike, and 

 consequent rivers ran out to sea over it, is remote and impossible to 

 trace. With the exception of the Goring gorge, which may be 

 otherwise explained, no connexion whatever exists between the 

 drainage-systems or the topography of the Cotteswolds and the 

 Chilterns, nor does a vestige remain of the peneplain which, at 

 some unknown height above the present surface, is supposed to have 

 united them. The escarpments form two dip-slopes, to which the 

 streams traversing them are respectively conformable. 



The more important rivers of Central England are longitudinal, 

 following the strike of softer rocks along which the predominant 

 erosion has taken place, the transverse drainage being everywhere 

 subsidiary to that of the plains. The excavation of the latter may 

 have taken place at a comparatively-early period in a direction not 

 vertical, but inclined more or less with the dip of the softer strata, the 

 formation of the dip-slope and the cutting-back of the opposing escarp- 

 ment being contemporaneous ; the erosion of valleys in the dip-slope 

 must have been posterior to this, and could not have preceded it. 



