lxxxiv PEOCEEDIXGS OF THE GEOLOGICAL SOCIETY, [vol. lxxv r 



and near enough to the Calvert Boring to render available its 

 definite information respecting the Jurassic sequence. Both borings 

 reached the Palaeozoic floor, and, if the line were prolonged beyond 

 Aylesbury for 30 miles or so farther east, it would intercept the 

 Ware Boring, in which the absence of all the Jurassic rocks was 

 proved, the Gault resting directly upon Silurian, It is the existence 

 of these borings, with then* positive evidence, that has impelled me 

 to adopt this line, though it is imperfectly adapted for comparison 

 with the Wealden section on the same scale, as it traverses the 

 strike of the Jurassic rocks obliquely, and is thereby inconveniently 

 lengthened, while the angles of dip are correspondingly decreased. 

 If it had been possible to take a shorter line directly south-eastward 

 from Gloucester, I believe that the resemblance of the sections 

 would have been much closer; but the underground^geology in this 

 direction has not yet been proved sufficiently to justify delineation. 

 The section now presented will, however, serve well enough for 

 mv general argument. It shows, in a less accentuated form, the 

 same wedge-like profile of all the Jurassic formations, and the 

 same fan-like arrangement of the dips ; but with this difference, 

 that the thick end of the wedge lies to the westward instead of to 

 the southward. At the western end, near Gloucester, the Lias 

 alone has a thickness of not less than 1360 feet ; at Burford, 

 22 miles to the east, it has shrunk to 627 feet ; at Calvert, 27 miles 

 still farther east (brought to the line of section at the perpendi- 

 cular), it is diminished to 210 feet, and must wedge out entirely 

 long before Ware is reached. The Lower Oolites, at their outcrop 

 on or near the line of section east of Gloucester, have a maximum 

 thickness of about 600 feet, which is reduced to a little over 

 100 feet at Calvert. 1 Most of the Middle and all the Upper 

 Oolites lie east of the borings, so that we do not know what 

 their thickness may have been in the tract from which they have 

 been stripped ; but they are, together, about 800 feet thick at their 

 outcrop along the line of section, and, if we grant them this thick- 

 ness only, without allowance for westward expansion, it will bring 

 up the original pile of Jurassic sediments in the Gloucester area to 

 a thickness not far short of 2800 feet. At Calvert the whole pile 

 is reduced to a thickness of about 1000 feet, and has probably 

 wedged out altogether 10 or 15 miles farther east, partly by 



1 The Burford Boring started below the top of the Lower Oolites, and proved 

 the remainder to be 90 feet thick, to which probably about 60 feet more should 

 be added for the portion removed by erosion. 



