272 Dr. FiTTON on the Strata below the Chalk. 



publication, it may perhaps deserve inquiry, whether some portions of it may not exist beneath 

 the sands in that quarter. 



Wealden. — The traces of the upper members of the Wealden, are here so rare and indistinct, 

 that nothing has yet come within my knowledge which can be referred to them, except on the 

 summit of Shotover Hill, where shells, supposed to be of freshwater species, are found above 

 the Portland strata, in a ferruginous sand or clay ;''and at Quainton and some other places in 

 Buckinghamshire, where grit like that of Hastings, contains Paludinae. 



The lowest of the Purbeck strata are here fully characterized by their fossils, and precisely 

 resemble the lower beds of this formation in the Vale of Wardour and on the Dorsetshire 

 coast. They consist of slaty limestone, like the " tilestone " of Ladydown in the Vale of War- 

 dour, and the " Slate " of the Sections in the Isles of Portland and Purbeck. With this stone, 

 beds of clay alternate, which become more frequent in approaching the Portland strata, and 

 clearly represent the " Dirt-beds " of that island and the adjacent coast. One of the lowest of 

 these clays, contains thin layers of a species of Mytilus (71/. Lyellii ?) which is found in several 

 detached points of the tract now under consideration. I did not, however, find in any of these 

 beds either silicified trunks of trees, or of the remains of Cycadeae ; but in the corresponding 

 place at Garsington in Oxfordshire, were detached fragments of silicified coniferous wood, like 

 that of Portland. In several cases the more uniform freshwater limestone in this lower part of 

 the Purbeck series is " Travertine " ; and like the " Cap " of Portland it includes cavities incrusted 

 with botryoidal carbonate of lime. 



The fossils which this formation affords here, as in the Vale of Wardour, are Cypris and Cyclas 

 in profusion, and of two or more species ; Mytilus and Modiola ; with, more rarely, Astarte 

 and Paludina of two or three species, and some minute spiral univalves. 



The Portland strata have been found in this part of England, throughout a tract between six 

 and ten miles in extent from south-west to north-east, on the line of its rise from beneath the 

 superior strata, (Pease Farm, near Great Hazeley, in Oxfordshire, to Bierton near Aylesbury, 

 Bucks), — and about five-and-twenty miles, on the course of its outcrop, (from Garsington in Ox- 

 fordshire to near Stewkley, Bucks). They, no doubt, constituted at one time a continuous group, 

 but having been cut through by irregular denudation, now exist principally in the upper part 

 of the detached heights, which are separated by low ground excavated in the Kimmeridge 

 clay. 



The Portland-stone makes its first appearance north of Swindon, on a line directed from 

 about south-east to north-west, through Easington, south of Little Milton and Garsington, 

 towards Oxford. On the south of that line no stone is found ; the villages of Chalgrove, Ascot, 

 Stadhampton, and Chiselhampton being supplied with it from the Milton pits. Among the points 

 where I have seen the Portland beds near their first rise from beneath the superior strata, are — 

 a spot near the brook between Peg's Farm and Standhill, on the south-east of Great Hazeley 

 (Section No. 18.) ; near Cotmore Walls, about a mile west of Thame (No. 19.); near the windmill 

 at Towersey, Bucks; east of Kingsey ; Haddenham Field, about half a mile west of the church; 

 about midway between Ford and Moreton's Farm; near Bishopstone; Pistol Hill, — the vicinity 

 of Walton, and of Broughton, near Aylesbury ; and the summit of the heights at Bierton. 

 Beyond this last-mentioned place, I could not learn that stone has yet been discovered; though, 

 as it occurs at Church Farm on the road from Wing to Cublington, it may probably be found 

 to rise between the chalk, at Ivinghoe and Totternhoe, and Wing. The Portland sand has been 

 quarried between Tinkershole and Stewkley, and about a mile north of Dunton ; and the out- 



