part 1] 



ANNIVERSARY ADDRESS OF THE PRESIDENT. 



lxxxix 



«nce with, the Jurassic structure, and has its axis over the thin part 

 of the wedge, near the Jurassic anticline, in the same way that the 

 Chalk syncline of the London Basin covers an older anticlinal area 

 where the Jurassic rocks are thin or absent. 



The general conditions in North Yorkshire are analogous to 

 those in the South Midlands also. The present broad outcrop of 

 the Jurassic rocks coincides roughly with a region of maximum 

 sedimentation, and there are indications that the deposits were 

 thinner in the north and west, where they have been removed by 

 denudation, as well as in the south, where we can still see something 

 •of them. As in the South Midlands, the basin as a whole has been 

 tilted by the differential uplift of the outer margin, but without 

 altogether eradicating the original syncline. 



Comparative Thickness. 



It is rather curious that, while the maximum thickness of the 

 three Jurassic wedges which we have had under consideration is in 

 •close agreement, the thickness of the component formations varies 

 widely. In the Weald, so far as is known, the Upper Oolites are 

 by far the thickest elements of the wedge ; in the South Midlands, 

 and in Yorkshire, this part is played by the Lias and Lower Oolites. 

 To bring out both the resemblance and the difference, I have 

 arranged in parallel columns in the following table, the maximum 

 known thickness of each Jurassic division in the three areas, on 

 or near the lines of section. 



Maximum known Thickness of the Jurassic Eocks in the 

 three Sections (figs. 2, 3, & 4, facing p. lxxx). 



I. 



Weald. 

 Formation. (Borings.) 



feet. 



Purbeck 562 1 



Portland 141 2 



Kimmeridge 1 2 73 3 



Corallian 342 4 



Oxfordian 191 4 



Lower Oolites 194 4 



Lias 140 4 



2843 2800 2780 



H. 



III 



South Midlands. 



Worth Yorkshire, 



(Outcrops.) 



(Outcrops.) 



10 







80 



— 



T300 



600 



\ - 



350 



(.450 



410 



600 



550 5 



1360 



870 



1 Penshurst Boring. 2 Battle Boring. 3 Sub-Wealden Boring. 



4 Brabourne Boring ; the thickness of these divisions is probably greater 

 in the middle of the Weald, but has not been proved. 



5 West of the Peak Fault ; east of this fault, the thickness is about 100 feet 

 greater. 



