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PEOCEEDTfreS OP THE GEOLOGICAL SOCIETY. 



[Jan. 23, 



As the beds below the last line of nodules were hidden by fallen 

 rubbish, I could not see the full thickness of the " rock." The beds 

 of nodules are two or three inches thick. 



Working eastwards, the next place at which I have seen the 

 Chalk-rock is in the neighbourhood of East Ilsley, in Berkshire, 

 where, indeed, I first noticed it. Here its thickness is not much over 

 4 feet. 



About half-way between Pangboum and Bassildon, in a large pit 

 on the Oxfordshire bank of the Thames, it is seen to be about 6 feet 

 thick ; and in the neighbourhood of Henley-on-Thames it is about 

 4 feet. At this last place, the Chalk-rock and the Lower Chalk occur 

 as an inlier, being surrounded on all sides by Upper Chalk. There are 

 three good sections on the northern side of the Thames between Henley 

 and Medmeuham. In these, as well as in the section above Pang- 

 bourn, its position in the Chalk is well shown. It forms an exact line 

 of division between the Upper Chalk (with flints) and the Lower Chalk 

 (without flints), — there being generally a bed of flints lying on its 

 upper surface, whilst there are none either in or below it, with the 

 following exception, which does not in any way disprove the rule. 

 In a chalk-pit just above Greenland Lodge, near Henley, there is a 

 section aeross a small fault, from which, below the Chalk-rock, 

 proceed two highly inclined fissures, some feet in length, but not 

 more than a quarter of an inch broad ; each of them is filled with 

 a liae of flint, which must clearly have been deposited from some 

 siliceous solution that found a channel down the fissures, and 

 which must therefore be of later date than those fissures. These 

 two lines of flint have no relation to the beds of flints in the chalk 

 above the " rock," but are inclined* at a high angle to the line of 

 bedding. 



Still working eastwards, the Chalk-rock may be occasionally seen 

 along the chalk-escarpment, at no great distance from the top, and 

 also on the flanks of the main valleys running at right angles to the 

 strike of the Chalk (and differing from the lesser valleys, which are 

 dry, in containing streams). 



As the dip of the Chalk is not much greater than the fall of these 

 valleys, the Chalk-rock does not disappear along them for many 

 miles inland from the escarpment. Thus, along the Loudwater 

 Valley it occurs as far south as Wycombe Marsh ; in the Misbourne 

 Valley it reaches to a point a little below Amersham ; along the 

 Chess Valley, to nearly three miles below Chesham; and in the 

 Berkhampstead Valley to some spot between Boxmoor and King's 

 Langley. 



Near High Wycombe, and to the east of that town, the Chalk-rock 

 loses its hitherto well-marked jointing, and breaks up into compara- 

 tively small pieces. In the neighbourhood of Wendover, Amersham, 

 and Berkhampstead, its thickness has dwindled down to 2 or If feet ; 

 but on the hills to the south-east of the first place there are two beds 

 of it, separated by a few feet of chalk. 



The last section of the Chalk-rock that I saw was in a pit near the 

 Boxmoor Railway-station, where for the first time I noticed beds of 



