462 PROCEEDINGS OF THE GEOLOGICAL. SOCIETY. [June 19, 



chalk, but over tlie under-terrace of upper greensand, as about Hinton 

 and Wanborougb, and considerably in advance of the chalk, as over 

 the area of Kimmeridge clay and coral rag. Many of these blocks 

 are of great dimensions, and have most probably sunk down vertically 

 to their present positions from their places in the eocene deposits, by 

 the removal of the intervening beds by denudation. 



Our time would not allow of detailed examination of the Portland 

 beds of Bourton, I therefore subsequently visited the place again ; 

 first alone, and again in company with Mr. Sharpe. The order of 

 the beds can be well traced on the east of the hill, and from above 

 downwards is as follows : — 



1 . Stratified earthy oolite. Ammonites, casts of Trigonice. 8 feet ? 



2. Buff-coloured sands, with bands of pale yellow sand. No fossils. 



12 feet. 



3. Flat-bedded, white, oolitic sand. No fossils. 8 feet. 



4. Rubbly oolite. Large Pleurotomarice. 1 foot. 



5. Thick-bedded fossiliferous band. 3 feet. 



6. Ostrea and Perna bed. 



7. Pebbles in calcareous beds. Fossils numerous. 10 feet. 



8. Fine sands. 7 feet? 



9. Kimmeridge clay. 



The bed No. 7 escaped our observation at our first visit. My at- 

 tention was called to it by the numerous and large blocks of conglo- 

 merate which are to be seen built into all the walls of the village of 

 Bourton : the lower levels of the quarry from whence they are taken 

 being filled with water, the succession of the beds cannot at all times 

 be observed there below the band of Ostrea and Perna, No. 6. They 

 are, however, to be seen in situ in the road section, and with their 

 underlying sands confirm the account which the quarryman gave me 

 of the lowest beds. The pebbles consist of subangular fragments of 

 white, transparent, and granular quartz, such as fine-grained sand- 

 stones are seen to become in proximity with intrusive crystalline rocks. 

 Much more abundantly there occur black pebbles of hornstone or 

 lydian, which contrast forcibly with the white calcareous cement 

 in which they are imbedded. In the conglomerate beds I met with 

 the internal cast of a bivalve shell (Cardimn), the material being 

 identical with that of the mass of black pebbles, showing that the 

 strata which have supplied this portion of the beds were altered se- 

 dimentary deposits, at the age and precise locality of which we may 

 therefore some day be enabled to arrive. The Fernce and Ostrece 

 form a band, as they do in the Swindon quarry ; and above occur 

 the principal fossiliferous beds. No. 5. The large Pleurotomarice also 

 form a distinct band. No fossils that I could discover occur through- 

 out the 20 feet of oolitic and siliceous sands, but they reappear in the 

 uppermost beds, consisting of casts of Trigonice with Ammonites gi- 

 ganteus, Sow., and A. hiplex, Sow., in great numbers. 



The series of Portland beds as here described are nearly hori- 

 zontal, and the blue Kimmeridge clay which is seen passing beneath 

 the sands and oolite on the north side of the hill, comes out from 

 beneath them on the south at a somewhat higher level than that of 



