222 



PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



Trigonia striata 

 Mactra gibbosa 

 Ampbidesma securiforme 

 decurtatum 

 Pholadomya ambigua 



lyrata 

 Modiola (four species) 

 Cucullaea oblonga 

 Perna mytiloides 

 Pecten vimineus 

 Terebratula perovalis 



Terebratula concinna 

 spinosa 

 resupinata 

 maxillata 

 and six others 

 Cirrus carinatus 

 Melania striata 

 Nautilus truncatus 

 Ammonites Parkinsoni 

 Browni 

 corrugatus 



These beds are capped with a band of sand and clay containing 

 nodular masses of oolitic stone, and a great number of Clypeus 

 sinuatus. 



5. Fuller's earth. This is a yellow argillaceous deposit, which 

 seems to be about 10 feet thick, but it presents few points of 

 interest. Its outcrop is marked by a line of springs. 



6. Stonesfield slate. This is the bed which it is the object of 

 the present memoir chiefly to describe.* 



Section. No. 1. 



6. Lower lias shales. 



5. Lias marlstone. 



4. Upper lias shales. 



3. Inferior oolite. 



2a. Fuller's earth. 



2. Stonesfield slate and ragstone. 



1. Beds of clay. 



The first quarries of this flagstone described are situated on the 

 top of a hill at Sevenhampton common, and the rock is generally 

 very rich in organic remains. There are here three quarries at 

 which the slate is worked, within the distance of half a mile from 

 one another. One of them exhibits about 15 feet of coarse fissile 

 ragstone, containing fossil remains of fishes and some shells, and 

 passing downwards into the true Stonesfield slate. In another 

 this ragstone, of about the same thickness, is occasionally inter- 

 mixed with slabs of hard slate having blue centres, and there is 

 then about 4 feet of true fissile Stonesfield slate, the upper slabs 

 of which are used for tiling ; but the lower part is sandy. 



* The authors consider that the beds so called were only partially known to 

 Mr. Murchison, and they disagree with some of Mr. Lonsdale's conclusions. 



