PORTLAND BEDS. 34 1 



There are several quarries along the coast at Dancing Ledge, 

 Seacombe, and Windspit. There is generally worked an upper 

 and lower freestone, shaped into blocks for building and into 

 troughs, etc. The general section of the beds is as follows : ^ — 



Shrimp-bed, fine-t^rained compact limestone 9 feet. 



Oyster-bed, with Ostrea soliiaria, Pcrna Bouchardi, etc 6 ,, 



Freestone, in two beds 35 ,, 



Cherty series. 



At Upway, north of Weymouth, the Portland Stone is a white 

 chalky-looking rock (white freestone), with nodules of black chert, 

 and it so much resembles the Chalk, that one might readily 

 imagine oneself to be in a Chalk-pit, until some of the fossil 

 MoUusca are noticed. Prof. Jones has observed Cretaceous 

 Entomostraca in this chalky rock.- Here the beds are highly 

 inclined to the north, forming the northern slope of the Weymouth 

 anticlinal. 



The Portland Beds of the Vale of Wardour, well shown in the 

 quarries of Chilmark ravine, north of Chicksgrove, are thus divided 

 by the Rev. W. R. Andrews : ^ — 



Feet. 

 Upper Cyrena-beds, white fine-grained oolitic limestone, in which 



the fossils occur as casts. Cerithiutn PortltDidiciim, Cyroia 



riigosa, Cardium, Lucina, Pecten, etc. NerttoDia sinitosa 



occurs sparingly 18 



Chalky series with flints (marine). Ammonites boloniensis, Trigonia 



gibbosa, Pecten, etc 24 



Lower Cyrena-beds or Ragstones (estuarine). Cyreiia rugosa, 



Neiitoma siniwsa, Cerithium, Lttcina, Cardium, etc 8 to lO 



Freestones or main building-stones, 4 or 5 beds of gritty limestone or 



calcareous sandstone with much glauconite, and sponge-spicules 1 8 



Basement Beds, impure sands, sandy limestones, and clay, with 



Trigojiia gibbosa, Mytilus jurensis, etc 38 



The Chalky beds may represent the ' Base bed' of Portland. They have been 

 used for hearthstones. 



The building-stones are known by the following local names (in descending 

 order) : Trough Bed, best building-stone. Green Bed, Pinney Bed, Hard Bed, and 

 Fretting Bed. Analysis of the Trough bed showed 10 percent, of silica, and 79 

 per cent, of carbonate of lime. 



Mr Hudleston was of opinion that there was some unconformity between the 

 Portland and Purbeck beds near Tisbury, but this appearance may be due to the 

 irregular nature of the several divisions of the Portland beds. 



The Upper Cyrena-beds were formerly quarried and used in the west front of 

 Salisbury Cathedral. The Chilmark freestone was used in the construction of 

 Salisbury Cathedral, Wardour Castle, Romsey Abbey, Rochester Cathedral, and 

 Wilton Abbey. At Chicksgrove, Wockley, Fonthill, and Tisbury, the beds are 

 worked in places. A band of chert opened up near Fonthill Giffard has supplied 

 many of the beautiful Corals (Isastma oblouga), polished specimens of which are to 



^ W. H. Hudleston and J. Morris, P. Geol. Assoc, vii. 382 ; Damon, Geol. 

 Weymouth, 1884, p. 87. 



" Q.J. xxxvi. 236; see also Fitton, T.G.S. (2),iv. 225. 



^ Proc. Dorset Nat. Hist. Club, v. 57 ; see also Fitton, T.G.S. (2), iv. 249 ; 

 W. H. Hudleston, G. Mag. 1881, p. 387, P. Geol. Assoc, vii. 173 ; J. F. Blake, 

 Q. J. xxxvi. 200. 



