42 



W. WHITAKEE ON SOME BOEIKGS IN KENT. 



So far all our evidence as to what underlies the Cretaceous beds 

 has been northward from the Yalley of the Thames ; and, indeed, we 

 have but one piece of evidence (besides that of the Chatham boring) 

 in the other direction, some way beyond the London Basin and 32 

 miles south of the Chatham site. This is from the Subwealden 

 Exploration-boring, the deepest by far in the south of England, 

 which, beginning in the Purbeck Beds, passed through a great 

 thickness of beds that are wholly unrepresented, not only in the 

 Chatham well, but also in all the others that have been referred to. 

 These beds show a regular continuous series through 180 feet of 

 Purbeck Beds, 60 of Portlandian, no less than 1120 of Kimeridge 

 Clay, and of Corallian &c. 480 feet, to Oxford Clay ; thus adding 

 1660 feet to the 1700 or more already shown to be wanting at 

 Chatham, not counting the Purbeck Beds, some 350 feet thick in 

 that neighbourhood, which have been already allowed for. In 32 

 miles we have therefore a loss of 3400 feet of beds, or a thinning 

 at the rate of rather more than 100 feet in a mile. 



It will be seen that this result bears out the leading idea of 

 Mr. Topley's paper, " On the Correspondence between some Areas of 

 Apparent Upheaval and the Thickening of Subjacent Beds"*, in 

 which it is said that " perhaps the most striking and most important 

 example of apparent upheaval being partly due to thickening of 

 strata, is that afforded by the Weald." Probably, howe\'er, the 

 underground thinning now recorded is much more than was reckoned 

 on ; though Mr. Topley went a long way towards the truth in one 

 of the sections on his Model of the Wealdt. 



I may here remark that the late Mr. S. V. "Wood, Jun., refused 

 to contribute to the fund for carrying on the Subwealden boring, on 

 the ground that he did not care to spend his money in sinking a very 

 deep hole in clays, which process he inferred would be the result of 

 the undertaking, and rightly, as the work was stopped at a depth of 

 1905 feet, when 65 feet deep in Oxford Clay. 



As regards the general bearing of the facts that have been 

 described, I think that it is simply in the line pointed out in 1880 

 and repeated last year J, and it may be put thus, in a few words : — 

 Whilst north of the Thames older rocks, as a rule, rise up beneath 

 the Cretaceous beds, on the south newer rocks come in between the 

 two, until, at our furthest point in that direction, these intermediate 

 formations have alone been found, to the greatest depth reached. 



There is little need to remind Eellows of this Society that the 

 subject has but lately been brought before them in detail by Prof. 

 Judd §. It is, however, so important, that one need not hesitate to 

 go over part of the same ground again, independently. 



As to the question of finding Coal Measures along the YaUey of 

 the Thames, it seems to me that a hopeful answer is possible, or at 



* Quart. Journ. Geol. Soc. vol. xxx. p. 186 (1874). 



t W. Topley and J. B. Jordan, Geological Model of the South-east of England 

 and part of France, including the Weald and the Bas Boulonnais (1873). 

 t ' Guide to the Geology of London,' ed. 2, pp. 20, 21, ed. 4, pp. 22-24. 

 I Quart. Journ. Geol. Soc. vol. xl. p. 724, and vol. xli. p. 523 (1884, 1885). 



