Vol. 69.] ANNIVERSARY ADDRESS OF THE PRESIDENT. lxXlii 



Wealden Anticline, which has been shown by Mr. Lamplugh to 

 have been superimposed upon a syncline. In fact, owing to the 

 swelling out of the Lower Cretaceous and Upper Oolitic rocks 

 under the arch, the anticlinal structure disappears downwards, and 

 is replaced in the Kimmeridge Clay by a gentle synclinal structure : 

 a relic, doubtless, of a more pronounced syncline which has been 

 flattened by the post-Oligocene movement. 1 The coincidence may 

 not be so strange as appears at first sight, for it is not infrequently 

 found that liability to movement, whether upward or downward, 

 is more or less confined to certain tracts. We can hardly suppose, 

 however, that the later warping has generally been so arranged as 

 to counteract precisely the effects of earlier movements. 



In the limited time at my disposal it is impossible to discuss the 

 effects of all the movements which have affected the platform since 

 its planation, and I propose to confine my remarks to the latest 

 and most energetic, those, namely, that came into operation 

 between Oligocene and Pliocene times, and were demonstrably 

 responsible for the geological structure of the South and East of 

 England. Eor the purposes of this investigation I have selected a 

 single plane in the Upper Cretaceous rocks, which has once been 

 horizontal or approximately so, and have endeavoured to ascertain 

 the magnitude of the distortions that it has undergone. 



The base of the Gault appeared, after some consideration, to be 

 the most suitable plane for the purpose. It is recognizable over 

 a wider area and with more certainty than any other, while by 

 choosing it I eliminated all the disturbances which had tilted the 

 Lower Cretaceous and Jurassic previously to the deposition of the 

 Upper Cretaceous rocks. It is true that the lowest beds of the 

 Gault are not always present, and that the assumption that the 

 plane was ever precisely horizontal and continuous would be 

 unsound ; but the departure from the horizontal is likely to have 

 been trifling in comparison with the figures with which we are 

 concerned, and insufficient materially to affect the conclusions. 



In the base of the Gault, therefore, I have determined the 

 altitude of as many points as possible, and from these data have 

 constructed a map (PL B, facing p. lxxviii) showing contours at 

 intervals of 500 feet, relative to the present sea-level. 



The data on which the contours have been drawn have been 

 derived from several sources. In the first place, the altitude of the 

 base along visible outcrops was determined at frequent intervals. 

 1 ' Mesozoic Rocks of Kent ' Mem. Geo!. Surv. 1911, p. 94. 



