Dr. FiTTON on the Strata below the Chalk. 249 



Ford; and their existence is rendered more probable, by the distinctness 

 with which the connected strata of the Purbeck group are developed ; the 

 whole series apparently thinning out towards the west. 



(132.) Purbeck Formation. — The Purbeck beds rise from beneath the sand 

 and clay at Dallard's Farm, near the eastern angle of the Vale of Wardour ; 

 and from that point they can be traced, — on the south of the Nadder, at 

 least as far as Totterdale, south of Tisbury ; and on the north, to Ashley 

 Wood, west of Ladydown, or perhaps to Stop Street, a hamlet above the 

 village of Ponthill Giffard ; occupying also the greatest part of the inter- 

 mediate heights between these extreme points. The strata throughout agree 

 with those of the coast; their fossils, with the exception principally of oysters, 

 belonging to freshwater genera ; and at the lower part near their junction 

 with the Portland stone, they likewise include beds of clay alternating with 

 limestone ; one of which at least contains the trunks of silicified trees. The 

 abundance of marine shells in the Portland beds immediately below, is here 

 as remarkable as in the Isle of Portland. 



The Map and Sections, PI. VII. fig. 3., and PI. X.a., fig. 13. a b &c., show the 

 general relations of the Purbeck series. The principal quarries open, in the 

 upper part of this formation, when I examined the country, were at Dallard's 

 Farm above mentioned ; at Dashlet on the south of the Nadder, about mid- 

 way between Catherine Ford and Chicksgrove ; and on the opposite bank 

 of the river, at TefFont Evias and near Legh-barn. The junction of the 

 Purbeck and Portland strata was best seen in a quarry at Wockley, on the 

 south-east of Tisbury, the counterpart of a much larger one, worked some 

 years ago at Chicksgrove (or Chilmark) Mill, but now obscured by decom- 

 position from long exposure. 



At Dallard's Farm, the beds first seen, on the west of the upper green-sand and gault, were 

 thus :— 



Ft. In. Ft. In. 



1 . Soil and Grass. 



2. Yellowish brown ferruginous loam, or clay 1 C 



3. Slaty stone and clay, including seams of fibrous carbonate of lime : 



a. Slaty limestone, containing Ostrea distorta, PI. XXII. fig. 2 6 



b. Fissile whitish calciferous clay, called " Spangle " by the quarrymen, Jn-l ^^ ^ 

 eluding great numbers of a small Modiola J 



c. Whitish uniform limestone, including Corhula alata, PL XXI. fig. 5., like"! _ 

 that near the coast at Upway J 



d. Fissile clay I 



e. Clay ; somewhat like d, but more approaching to stone 6 



/. Fissile clay, like " Spangle ", with Modiolae, like those of 6 1 4 g 



2k2 



