168 EEV. A. lEVING ON THE STEATIGRAPHT 



Cross Hills. There are traces of the pebble-bed all over the cap of 

 the hill ; the upper clays are exposed in a disused brick-field, a little 

 way to the south-west, and there are some exposures both of this 

 clay and of the underlying green earthy sands in several road- 

 cuttings ; a pond at the bottom of the hill (western side) is most 

 likely on the lower clays of this Group. At quite a high horizon 

 (certainly above the green sands) there is an exposure in a sand-pit 

 of some of the most strongly ' false-bedded ' sands * to be found 

 anywhere. A similar instance was observed lately in a sand-hole 

 behind the "Wellington Hotel near Wellington College Station. 



The section of the Lower Sands at Stroud Green (Quart. Journ. 

 Geol. Soc. vol. xlii. p. 40Jt), at about 50' O.D., the section in the 

 cutting north of A'irginia-Water Station (with a line of pebbles and 

 some slightly carbonaceous shales), and the 110 feet of sands pierced 

 in the well at the Holloway Sanatorium t, show that they thicken 

 out in the direction of St. Anne's Hill, where they probably attain 

 their full normal development. 



It will be observed that the foregoing sections of the Middle 

 Group, showing the outcrop along the northern flank of the main 

 mass of the formation, are all on the same line of outcrop as 

 section E of my last paper. The direct correlation of them with 

 the same group of beds in the Wellington-College Well is therefore 

 a comparatively easy matter. 



The I^oetheen- Lzn^e op Hills. (See Pig. 2 of my former paper.) 



In considering the progressive, though not uniform, subsidence 

 which admitted of the formation of the estuarine series hitherto 

 known as the Bagshot Beds of the London Basin, I think that the 

 evidence now before us, furnished by recently and formerly 

 published deep-well sections, justifies us in considering the river- 

 sands of the Lower Group as deposits formed in the silting-up of 

 the more central parts of the London-Clay estuary ; and that while 

 the process was going on, the London Clay was in part exposed to that 

 amount of denudation and erosion which we should expect on the 

 margin of an estuary, evidence of such displacement as we should 

 require for this being furnished in the Warfield Brick-yard. (See 

 Section P of my last paper, Quart. Journ. Geol. Soc. vol. xliii. 



* Another very fine example of false-bedding (oblique lamination) is seen ia 

 a section high np in the Upper Sands near the Eifle-butts, N.E. of Ash Vale 

 Station. There is also much pipe-clay in thin lamina. Such facts will be seen 

 at once to discount largely the importance of these structural phenomena, on 

 which so much stress has been laid, as evidence of horizons. 



t WTiitaker, ' Surrey Wells and their Teaching,'p. 66. I doubt the correctness 

 of assigning the whole 110 ft. to the Lower Sands, as at Holm Lea, the residence 

 of my friend Dr. Ginsburg, I have lately seen a capping of flint pebbles, and 

 below these a strong clay-and-sand bed (proved to 12') laid bare in excavations. 

 The layer of pebbles (at a lower horizon), which is seen in the railway-cutting, 

 is seeu also in the fine white sand in a lane on the north flank of the hiU.. 

 The clay-and-sand bed (which I regard as=]S'os. 9 & 10) runs, I believe, through 

 Callow Hill, its base being seen at the top of a sand-pit in Hunter's Dale, 

 where 18' of the quartz-sand series (Nos. 11 & 12) are exposed. 



