lxxxviii PEOCEEDIXGS OF THE GEOLO&ICAL SOCIETY. [vol. IxXV, 



Pocklington by the unconformity ; the Oxfordian and Corallian 

 together count some 750 feet where they can he measured in 

 Xewtondale, but have shrunk to 90 feet under the "Wolds ; the 

 Kimmeridge Clay may be 600 feet thick in the Yale of Pickering 

 but is shaved off soon after it passes beneath the Chalk. Assuming 

 that the formations were originally continuous up to the northern 

 limits of our section with the same thickness as at their present out- 

 crop, there has been, in the north, a column of sediments 2700 feet 

 thick against a column of only about 350 feet in the south ; and 

 the wedge was later sharpened down almost to a feather-edge by 

 Cretaceous erosion. The Lias and Middle and Upper Oolites of this 

 area are broadly similar in character and origin to those of the South 

 Midlands and Kent ; but the Lower Oolites, which bulk largely in 

 the middle part of the wedge, are quite different, estuarine sand- 

 stones and shales taking the place of the marine beds of the south. 

 There is clear evidence, however, that the whole sequence was 

 deposited under the same tectonic conditions of a long-subsiding 

 trough. Intercalated with the estuarine beds are some narrow 

 hands of shallow-water marine sediments, which, along with the 

 Corallian beds of the Middle Oolites, afford old horizon-planes as 

 definite as those in the south ; and these show in section the same 

 fan-like arrangement, though with a different radiant. They 

 demonstrate that, throughout the Jurassic Period, there has been 

 in this area a recurrent sinking in the north and north-west with 

 relative stability in the south and south-east. 



The resemblance in structure is carried still further, for here 

 again we find the deep syncline beneath the heaviest pile of sedi- 

 ments, and the aprise where the wedge thins beneath the Chalk. 

 The bottom of the syncline underlies the Yale of Pickering, where 

 it probably descends to at least 1500 feet below sea-level (see fig. 4, 

 facing p. lxxx), and from this depth rises rather sharply to the south 

 towards the pre- Cretaceous anticline at Market Weighton. But it 

 is only on the western flank of the Wolds, by the accident of the 

 recession of the Chalk escarpment, that this structure is revealed. 

 In traversing the east coast from Eobin Hood's Bay to Holder- 

 ness, we encounter a steady persistence of southward dips, and a 

 regularly ascending sequence from Lower Lias to L'pper Cretaceous. 



We cannot tell what the attitude of the Cretaceous cover may 

 have been when it extended northwards over the syncline, but it is 

 noteworthy that a shallow syncline in the Chalk, well brought out 

 by the bold curve of the line dividing the flintless Upper Chalk 

 from the flinty Middle Chalk on the Wolds, shows no correspond- 



