C— GEOLOGY. 71 



To the northward of it, the axis of Le Catelet with a westerly pitch 

 becomes an insignificant structure farther west, and ultimately becomes a 

 mere wrinkle on the south flank of another anticline, between Saulty and 

 Bapaume, which in its turn disappears both eastward and westward. 

 North of Amiens another anticline rises on the line Valheureux-Bernaville, 

 which in its turn disappears in both directions ; its continuation to the 

 east almost coincides with the syncline between the Le Catelet and 

 Rosieres anticlines. 



Finally, in the northern part of the area considered by Mr. King, the 

 main axis of elevation is that of the Vimy Ridge which is completely lost 

 eastward in a region of indefinite structure between Douai and Cambrai. 



I have no doubt that if any horizon in the Upper Cretaceous rocks of 

 the Wealden area were similarly contoured, it would disclose a type of 

 folding identical with that of the post-Cretaceous folding in Northern 

 France. The study of the Weald and of Northern France reveals the 

 major characteristics of the folding to be as follows : — (1) The anticlinal 

 axes are impersistent and tend to be arranged en echelon. (2) The 

 structures are in general most sharply defined near the points of maximum 

 elevation ; in the lower-ljring regions of the folded surface, particularly in 

 those areas where the anticlines change their pitch, a simple fold is in 

 general replaced by minor wrinkles. 



Mr. King and others have called attention to the general correspondence 

 between the folding and the drainage lines of the area, and in particular 

 between the trend of the major streams and the main synclinal depressions, 

 though Mr. King points out that the courses of the streams do not coincide 

 %vith the 5}Ticlinal axes but usually lie somewhat to the north of them. 



Having studied the general characteristics of the movements which 

 affected the later Mesozoic rocks of the south-east of England and Northern 

 France, let us direct our attention to the folding that has affected the 

 earlier Mesozoic rocks of the Bristol Channel region. 



Unfortunately the only formation of that age which reaches the coast- 

 line of the Bristol Channel is the Liaa, and even of that formation only the 

 lower portion is represented. In general the Lias succeeds conformably 

 a thin development of Rhaetic, and this in turn overlies Keuper which 

 rests with marked unconformity on the Palaeozoic floor. Although there 

 are indications here and there of minor interruptions at the boundary 

 between the Keuper and the Rhaetic, the relation of these formations 

 as a whole suggests conformity. Over large areas the Lias and Rhaetic 

 have been removed by subsequent erosion, leaving the surface occupied by 

 Keuper. In view of the relations between the formations it may be 

 assumed, however, that wherever Keuper occurs at present it was formerly 

 succeeded by Rhaetic and Lias. The converse, however, does not hold. 

 There are many places where the Lias or Rhaetic rests directly upon 

 the Palaeozoic rocks without the intervention of the Keuper. These are 

 areas where the uneven surface of the Palaeozoic floor projected as islands 

 out of the Rhaetic or Lias sea, and were only submerged during the depo- 

 sition of the later Liassic strata. The regions which lend themselves most 

 conveniently for study are the Vale of Glamorgan and the Mendip region. 



Vale of Glamorgan. — In the Vale of Glamorgan the normal succession 

 of Lias-Rhaetic-Keuper prevails for some miles west and north of Cardiff. 



