432 



MR. H. Gr. LYONS ON THE LONDON CLAY 



I first propose to discuss one particular section which has "been 

 very differently interpreted by different observers *. 



The section is one through Thorn and Redan Hills to the east of 

 South Camp, and, as shown in fig. 1, is drawn in a direction ~N. 14° E. 

 and S. 14° W., thus giving nearly the true dip of the beds, which 

 dip slightly E. of N. ' 



Commencing at the North end of the section (which is drawn on 

 the scale of 4" to one mile horizontal and 8" to one mile vertical), 

 the Pebble-bed, which I take as the line of division between the 

 Upper and Middle Bagshot, occurs behind the Commissariat Stores, as 

 described by Mr. Monckton (loc. cii. p. 410). 



This bed of rolled black flint-pebbles can be traced round the east 

 slope of the hill past the Magazine and the Cemetery, at each of 

 which places it can be seen in situ, to the brow of the hill on which 

 the Cambridge Hospital stands. Here the bed has rather thinned 

 and the pebbles are imbedded in a more clayey bed than at the 

 Commissariat Stores. 



Walking down the road leading from the eastern end of the 

 Hospital enclosure to the Field Stores in the valley below, we 

 start from the pebble-bed at the top and pass over the outcrop of 

 the different beds of the Middle Bagshot, and then of some of the 

 Lower Bagshot. 



The upper portions of the Middle-Bagshot beds are at first sandy, 

 as we see in nearly all the well-sections in the neighbourhood, but 

 lower down the} T become stiff and clayey, till at the foot of the hill the 

 sandy Lower Bagshots come in. Behind the Field Stores 20 ft. of 

 white, false-bedded Lower-Bagshot sand appear in a sand-pit ; and 

 as we ascend the slope of Bedan Hill, wherever rifle-pits or shelter- 

 trenches furnish us with sections, yellowish sands of the Lower 

 Bagshot are seen. 



A shelter-trench made last summer furnishes a good section of 

 the upper third of Redan Hill, and in it we find exposed, first the 

 yellowish sands of the Lower Bagshot, then clayey beds similar to 

 those passed over in descending the opposite slope of Thorn Hill. 

 These clay-beds extend to the top of Redan Hill till overlain by the 

 gravel capping above them ; and I take them to be the lower beds of 

 the Middle Bagshot, which have been raised to this height by the 

 northerly dip of all the Tertiary beds. I will show presently that 

 this is sufficient to do so. 



On the south side of Redan Hill these clay-beds are almost 

 wanting, being only seen quite at the top of the railway-cutting, 

 where they are brought out by the northerly dip of the beds. The 

 pebble-bed described by Mr. Irving as occurring in the railway- 

 cutting south of Redan Hill appeared to be a few scattered pebbles 

 occurring at a particular horizon in the Lower Bagshot. Thus 

 there should be no anticlinal between Thorn Hill and Redan Hill as 

 shown by Mr. Irving ; and the section as drawn by Messrs. Monckton 

 and Herries in their paper (Quart. Journ. Geol. Soc. vol. xlii. 

 p. 412) requires some alteration. 



* Eev. A. Irving, Quart. Journ. Greol. Soc. vol. xli. p. 502 ; and Messrs. 

 Monckton and Herries, Quart. Journ. Geol. Soc. vol. xlii. p. 410. 



