I 



TRANSACTIONS OF SECTION C. 859 



escai-pment. At that time it was not fully realised that the Inferior Oolite in 

 the Bath district is, for the most part, limited to the Parki/iso7ii-zone, so that the 

 comparison was really being made between beds of different age as well as different 

 physical conditions. The question resolves itself into one of local details, which 

 are not suited for a general address. Still, I think it may be taken for granted 

 that, notwithstanding the east-and-west barrier of the Mendip range, which acted 

 effectually previously to the Parkinso?ii-o\eYla.'p, there was in some way a com- 

 munication by sea between Dundry and Dorsetshire, more especially during the 

 >So2ierby>~sta.(:^e, and this most probably was effected round the western flank of the 

 Mendips. Thus, without acceding to the necessity for a barrier facing the Southern 

 Cotteswolds, we may readily believe that much of the Inferior Oolite of Dundry 

 Hill is to be regarded as an outlying deposit of the Anglo-Norman basin. If this 

 1)8 so, it is difficult to avoid the conclusion that the low-h-ing area of the Bridge- 

 water flats was, diiriug part of the Inferior Oolite period, occupied by a sea which 

 was continuous from Sherborne to Dundry, and that, although the barrier of the 

 Mendips was interposed, communication was effected round the west flank of that 

 chain. This would make a portion of the Bristol Channel a very ancient feature. 



We must now take a wide leap in time, passing over all the rest of the Jurassics, 

 and just glancing at the Upper Cretaceous system, which reposes on the planed- 

 down surface of the older Secondary rocks. The remarkable double unconformity is 

 nowhere better shown than in the South-west of England. Some of the movements 

 of the older Secondary rocks, prior to the great revolution which brought the 

 waters of the Cretaceous sea over this region, have been successfully localised hy 

 Mr. Strahau, more especially in the south of Dorset. 



Owing to Tertiary denudation the Chalk in this immediate district has been 

 removed, and we have no means of judging the relations of the Cretaceous deposits 

 to the Palreo/.oic rocks of Wales. If we may judge by results recently recorded 

 from Devonshire,' the Lower Chalk especial!}' undergoes important changes as it 

 is traced westwards, and generally speaking terrigenous deposits seem more 

 abundant in this direction. At the same time the more trulj' oceanic deposits, 

 such as the Upper Chalk, appear to be t binning. 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 Rock," which has been found 

 especially rich in Gasteropoda at Cuckhamsley, near Wantage. 



Tertian/, Fleisfoce/ie, and Recent. — 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 Dorsetshire, 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 accumu- 

 lated shingle, becomes the plateau of another period — an endless succession of 

 revolutions further complicated by the Pleistocene 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 PalEeozoic rock, has produced both the Jurassic and Cretaceous escarp- 

 ments as well as the numerous gorges which add so much to the interest of the 

 scenery. These phenomena have been well described by Professor SoUas,' when 

 he directed an excursion of the Geologists' Association in 1880. Should any student 

 wish to know the origin of the gorge 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. 



' Cf. Jukes-Browne and Hill, Qvart. Journ. Gcol. Soc. vol. Hi. (1897), p. 99. 

 2 Quart. Journ. Geol. Soc. vol. lii. (1897), p. 68, and vol. liii. (1898), p. .377. 

 ' Froc. Geol. Assoc, vol. vi. (1881), p. 375. 



