202 



ME. W. WHJTAKEE ON THE EESULT 



Wealden 



(continued). 



Thickness 

 in feet. 



Dark clay with pyrites. Specimens, 

 grey clay at 895 and 898 4 



Hard dark clay. Specimens, grey clay 

 at 899, 900, 901, and 933, some with 

 pale sandy specks 7 



Brown clay. Specimens, grey clay at 

 906; pale grey pipe-clay, with pale 

 very fine-grained sandy lumps, the 

 whole whitish and calcareous in 

 appearance, but not so really 6 



Dark clay, with rag-boulders. (? Some 

 error here, specimen at 913 being of 

 whitish earth, like the last ; ? former 

 account more correct.) Specimens, 

 grey clay, with light-coloured patches, 

 at 915 ; grey clay at 917 (one piece 

 sandy) and 918 14 



Very light-coloured clay 5 



Darker clay. A small specimen, marked 

 937 (? should be 927), is light-grey 

 ^ clay, rather sandy ? 1 



On comparing the Dover section with that of Chatham (described 

 in my former paper), we see that the undergonnd thinning of the 

 Lower Cretaceous beds has gone further at the latter place than at the 

 former, except as regards the Lower Greensand, which is 41 feet 

 thick at Chatham, where two divisions (the Folkestone Beds and the 

 Sandgate Beds) are represented, whilst at Dover we have but 31 

 feet, of Sandgate Beds only. 



At Chatham, however, all the Cretaceous beds below this have 

 vanished altogether, neither Weald Clay nor Hastings Beds having 

 been found : but at Dover the latter series occurs, for the first time 

 in any of the deep borings in the London Basin, and has not yet 

 been pierced through. 



In drawing my transverse section, through Chatham, the Hastings 

 Beds were shown as thinning out before the Weald Clay, that 

 seeming to be the more likely event. The reverse is now proved 

 to be the case at Dover, and this may hold at Chatham also. 



The absence of the Weald Clay is perhaps less remarkable at 

 Dover than at Chatham, for whilst the thickness at the outcrop 

 south of the latter place seems to be about 600 feet, Mr. Topley 

 remarks that " we have at present no means of estimating the 

 thickness of the clay further east [than the neighbourhood of 

 Maidstone], but it probably thins regularly in that direction, and 

 may not be more than 350 feet thick near Hythe " *, the nearest 

 outcrop to Dover, which place, moreover, is still further eastward. 



It may be of use to notice here the probable thickness of the 

 various divisions of the Hastings Beds at the outcrop south-west of 

 Dover. These are as follows, beginning at the top : — The Tunbridge 

 Wells Sand, 150 feet or more ; the Wadhurst Clay, perhaps 100 feet; 



* " The Geology of the Weald," to which Memoir I am indebted, also, for 

 the thickness of the divisions of the Lower Greensand given above, and of the 

 divisions of the Hastings Beds. 



