part 1] aNjSTvebsAby address of the president. lxxxvii 



tions are the same as in North Kent. North of the Wash the 

 question becomes more problematic, but the composition and 

 structure of the Lower Cretaceous succession in Lincolnshire, and 

 the attenuation of the Lias and Oolites, suggest an approach to 

 the margin of the trough. 



The Yorkshire Jurassic Wedge. 



Crossing the Humber, we will pass to the consideration of the 

 other Jurassic area which Topley brought into comparison with 

 the Weald, namely, that of the North Riding of Yorkshire ; and 

 here again we shall find that the similarity is closer than he knew. 

 In this tract the strike of the rocks swings round, from a general 

 northward to a general eastward trend, in fact almost resuming the 

 direction of their hidden course in Kent. We do not gain much 

 help from borings in this region, as the Palaeozoic floor has nowhere 

 been attained within the Jurassic tract ; but the general structure 

 is revealed in the broad outcrops of the eastern moorlands and. in 

 the fringe emerging on the eastern side of the Yale of York, where,, 

 fortunately, the Chalk escarpment crosses the strike of the Oolites 

 and Lias, and has been cut back far enough to allow an insight 

 into the conditions beneath it. Here again we discover that the 

 Jurassic rocks as a whole form a huge recumbent wedge, of which 

 the apex points southward, that is, nearly at right angles to the 

 South Midland wedge, and directly opposite to that of the Northern 

 Weald. JFor an illustrative section I take a line running from 

 Robin Hood's Bay south-south-westwards to the edge of the Yale of 

 York near Pocklington, which will cut off a small slice of the Chalk 

 Wolds near the escarpment, where the evidence is clear (fig. 4, facing 

 p. lxxx). A longer line from the mouth of the Tees south-south- 

 eastwards to Market Weighton, perhaps better suited for comparison 

 with the previous sections, would have shown us the same structure 

 in a slightly less accentuated form, and more interrupted by irre- 

 gular topography. In the section used, the thinning of all the 

 members of the Jurassic sequence in the same direction is fully as 

 marked as in the previous sections. Taking the thickness of each 

 formation in turn as we cross its outcrop, we find that in the north 

 the Lias measures about 900 feet, but diminishes southwards to- 

 about 150 feet before reaching the Cretaceous unconformity, and 

 is then nearly cut out ; the Lower Oolites are at least 550 feet 

 thick at their outcrop on the moorlands, but dwindle down to 

 not much over 100 feet before they are shaved off north of 



