as President, to the Geological Section. 469 



same time tlie more truly oceanic deposits, such as the Upper Chalk, 

 appear to be thinniag. As regards the possible depths of the 

 Cretaceous sea at certain periods, we are supplied with some 

 interesting material in Mr. Wood's two papers on the Chalk Eock,^ 

 which has been found especially rich in Gasteropoda at Cuck- 

 hamsley, near Wantage. 



Tertiary, Pleistocene, and Becent. 



Although the Tertiaries of the Hampshire basins are within the 

 " Index Map " which we have been considering, they may be 

 regarded as beyond our sphere. Some of the gravels of Dorset- 

 shire, which have gone under the name of plateau gravels, are held 

 by Mr. Clement Reid to be of Bagshot age. Many of the higher 

 hill gravels most likely date back to the Pliocene, and even further, 

 and represent a curious succession of changes, brought about by 

 meteoric agencies, where the valley-flat of one period, with its 

 accumulated shingle, becomes the plateau of another period — an 

 endless succession of I'evolutions further complicated by the Pleisto- 

 cene Cold Period, which corresponds to the great Ice Age of the 

 north. 



In the more immediate neighbourhood of Bristol, since some date 

 in Middle Tertiary time, the process of earth-sculpture, besides 

 laying bare a considerable amount of Palaeozoic rock, has produced 

 both the Jurassic and Cretaceous escarpments as well as the 

 numerous gorges which add so much to the interest of the scenery. 

 These phenomena have been well described by Professor Sollas,^ 

 when he directed an excursion of the Geologists' Association in 1880. 

 Should any student wish to know the origin of the goi-ge of the 

 Avon at Clifton, for instance, he will find in the Report an excellent 

 explanation of the apparent anomaly of a river which has been at 

 the trouble of sawing a passage through the hard limestone, when 

 it might have taken what now seems a much easier route to the sea 

 by way of Nailsea. 



The origin and date of the Severn Valley is a still bigger question, 

 and this was broached by Ramsay, some five-and-twenty years ago, 

 in a suggestive paper on the Rivei'-courses of England and Wales.^ 

 He there postulates a westerly dip of the chalk surface, which 

 determined the flow of the streams in a westerly direction towards 

 the long gap which was being formed in Miocene times, near the 

 junction of the Mesozoio with the Palaeozoic rocks. The still 

 more important streams from the Welsh highlands had no doubt 

 done much towards initiating that gap ; and by the end of the 

 Miocene period, if one may venture to assign a date, the valley 

 of the Severn, which is one of the oldest in England, had already 

 begun to take form, though many of the valleys of Wales are 

 probably much older. 



1 Quart. Journ. Geol. Soc, yoI. Hi (1896), p. 68, and toI. liii (1897), p. 377. 



2 Proc. Geol. Assoc, vol. vi (1881), p. 375. 



2 Quart. Journ. Geol. Soc, vol. xxviii (1872), p. 148. 



