208 Dr. FiTTON on the Strata below the Chalk. 



Beds on the confines of the Hastings sand and the Purheck strata, at Worbarrow Bay*. 



Paces. Paces. 



Grey sand, occupying on the shore .... 8 



Yellowisli sand 5 



A space concealed at top ; where visible 

 the beds consist of grey clay, bitumi- 

 nous or carboniferous, which includes at 

 the bottom concretions of quartzose 



grit, and contains Cyclades 9 



A group including beds of stone com- 

 posed of small Paludinae, in a cement 

 containing much green matter : — the 

 "marble" and "marble-rag" of the 



Swanage quarry-men 16 



Brown and grey clay, alternating with bluish 

 grit, and thin beds of stone .... About 25 



Clay and limestone, including the "Lean- 

 ing vein " of the quarries on the east of 

 Purbeck. {^Quce. the "Lane-end Vein" 

 of Mr. Webster ?] 



Here the ground rises into the promi- 

 nence called Worbarrow Knob ; and the 

 back on top of a very extensive mass of 

 stone is waved, like the ripple-mark on 

 the sea-shore. Li the little cove between 

 the "knob" and Gad Cliflf, a thickness 

 of about 50 feet consists of clay, alter- 

 nating with beds of limestone very much 

 contorted. 



(104.) Purbeck strata. — The ridge of the Purbeck and Portland strata 

 runs nearly from east to west, entirely across the peninsula ; but the dip is 

 not uniform, and the strata form a curve, or a portion of a dome-like promi- 

 nence, of which the highest part is between Acton, St. Alban's Head, and the 

 heights above Kimmeridge, and thence to Tineham Hat ; the culminating 

 point being about Swyre Head, which seems to be about 700 feet above the 

 sea, — nearly on a level with the chalk down at the western extremity of Pur- 

 beck Hill, and perhaps 100 feet higher than the summit of Ballard Downf. 



The whole of the Purbeck series is exposed in the ruinous cliffs of Durl- 

 stone Bay, where the strata have been enumerated in detail by Mr. Webster;];. 

 At the upper part they consist of compact limestone, alternating with clay, 

 and abounding in freshwater shells, especially of the genus Cyclas : but in- 

 cluding also a thick bed called '' cinder " by the quarry-men, which is almost 

 entirely composed of oyster-shells. At the lower part, the formation consists 

 principally of fissile limestone, the junction of which with the Portland strata 

 exhibits some very remarkable appearances. 



All the stone which is quarried at present, occurs in the upper part of the 

 series ; and from Mr. Webster's list it appears that in a thickness of about 

 125 feet, 55 consist of beds of useful stone ; 12 feet of the "^cinder" composed 

 of oyster-shells ; and the remaining 58 of slaty clay, and thin beds of unpro- 

 fitable stone. I was informed that about 150 feet more, of what the work- 



* This is the spelling of the Ordnance Map, and the word is so pronounced in the country. It 

 is sometimes printed ^Far-borrow, and by Mr. Webster, Worth-harrow. 



■f The top of the Down between Acton and Bottom, (about the place of the final s in " Down- 

 shay's Farm ", in the Ordnance Map), is much higher than St. Alban's Head, and not much below 

 Swyre Head. It seems to be nearly level with Encombe Head (Hound's-Tout), and the east 

 end of Ballard Down. 



J Geol. Trans. 2nd Series, vol. ii. pp. 38, 39. 



