468 Notices of Memoirs — British Association — 



Beyond that neighbourhood, howevei', geologists are not in such 

 accord, and generally speaking, fairly good reasons can be given 

 both for and against the selection of many tracts for trial, except 

 in and near London, where no geologists would recommend it, from 

 the evidence in our hands. 



Let us then shortly review the evidence that we have on the 

 underground extension of the older rocks in South-eastern England, 

 with a view of considering the question of the possibility of finding 

 Coal-measures in any of the folds into which those rocks have 

 probably, nay almost certainly, been thrown. 



The area within which the borings that reach older rocks in the 

 London Basin is enclosed is an irregular pentagon, from near Dover, 

 on the south-east, to Eichmond on the west, thence to Ware, thence 

 to Culford on the north, thence to Harwich, and thence southward 

 to Dover, the greatest distance between any borings being from 

 Dover to Culford, about eighty-six miles. It is therefore over 

 a large tract, extending, of course, beyond the boundaries sketched 

 above, that we have good reason to infer that older rocks are 

 within reasonable distance of the surface, nowhere probably as 

 much as 1,600 feet, and mostly a good deal less. 



We must now consider some evidence outside the tract hitherto 

 dealt with. Southward of the central and eastern parts of the 

 London Basin we have evidence that the Lower Cretaceous beds 

 thicken greatl}^, from what is seen over their broad outcrop 

 between the North and South Downs. We know also, from the 

 Dover and Chatham borings, that the Upper and Middle Jurassic 

 beds come in to the south-east, whilst the Sub-Wealden Exploration, 

 near Battle, proves that those divisions thicken greatly southward, 

 the latter not having been bottomed at the depth of over 1,900 

 feet at that trial-boring. 



Westward, however, near Burford in Oxfordshire, and some miles 

 northward of the nearest part of the London Basin, Carboniferous 

 rocks have been found at the depth of about 1,180 feet, these being 

 separated from the thick Jurassic beds (including therein the Liassic 

 and Khgetic) by perhaps 420 of Trias. They consist of Coal- 

 measures, which were pierced to the depth of about 230 feet. 



In and near Northampton, north-eastward of the last site, and 

 still further from the northern edge of the London Basin, the like 

 occurs ; but the beds found are older than the Coal-measures, and 

 the Trias is thin, not reaching indeed to 90 feet in thickness, and 

 being absent in one case. At one place, too, the Carboniferous 

 beds have been pierced through, with a thickness of only 222 feet, 

 when Old Ked Sandstone was found, and in another place still 

 older rock seems to have been found next beneath the Trias. The 

 depth to the rocks older than the Trias, where they were reached, 

 was 677, 738, and 790 feet, or respectively 395, 460, and 316 below 

 sea-level. Some of these figures must be taken as somewhat 

 approximate, though they are near enough to the truth for practical 

 purposes. 



A boring at Bletchley, to the south, reached granitic rocks at the 



