396 PROCEEDINGS OE THE GEOLOGICAL SOCIETY. [Feb. 29 



thin laminae, between which innumerable shells of Ammonites pla- 

 norbis He closely compressed; the white decomposed pulverulent 

 matter of the shell forming a strong contrast to the dark shales which 

 enclose them. In Somersetshire the rock consists, at Uphill, of shales 

 which greatly resemble those at Brockeridge ; at Watchet, of dark 

 clays which are more indurated and have preserved better the shell- 

 structure : here Ammonites planorbis and Am. Johnstoni are found 

 with the iridescent nacreous layer of their shells beautifully pre- 

 served. At Street the rock is a light-yellowish clay, with bands of 

 greyish limestone and marl beneath, and in Worcestershire at Stren- 

 sham, and in Warwickshire at Binton, similar lithological conditions 

 prevail. 



The White Lias series of the Section at Saltford (see p. 400) repre- 

 sents the Am. planorbis beds : here also the relation of that zone 

 to the Saurian beds below, and to the Am. BucMandi beds above are 

 well shown. In Dorsetshire the Am. planorbis beds are represented 

 by the White Lias which is so well exposed in the large quarries at 

 Up-Lyme, and in the coast-sections at Pinhay Bay and Axmouth, 

 The White Lias is raised at Up -Lyme for caustic lime ; it consists of 

 a fine-grained cream-coloured limestone, apparently fit to be used as 

 a lithographic stone. The two principal quarries afford the neces- 

 sary details. Mr. Webb's quarry shows : — 



1. (Uppermost.) The "Wetstone" (8 feet); consisting of thin 

 bands of light-coloured limestone, interstratified with beds of clay. 

 I collected Lima gigantea, Sow., and Lima antiquata, Sow., from the 

 limestones. 



2. The " Grey Bur " (14 inches) ; a good building-stone, con- 

 sisting of two beds. 



3. The " Rotten Bur " in two beds (6 inches) ; valueless, falling 

 to pieces when exposed to the air. 



4. The " Fire-stone " in two beds (6 inches) ; forming good flag- 

 stones. 



5. The (i Cliffage " (4 inches) ; worked for paving-stone ; the 

 surface of the rock is covered with many small Oysters (Ostrea 

 Zv ctHm cci) 



6. The " Half foot" (6 inches) ; 7. the " One foot " (12 inches) ; 

 8. the " Bed Size " (7 inches) ; and 9. the " Anvil-edge" (18 inches) 

 — are all employed for building-stones. 



10. The " White Lias " (20 feet exposed) ; a compact earthy lime- 

 stone, with a conchoidal fracture, cream-coloured and fine-grained ; 

 many of the beds are so hard and close-grained that it might be 

 employed for the purposes of lithography. It contains very few 

 fossils ; sometimes specimens of Ammonites Johnstoni, Sow., are 

 found in the marl-seams. The White Lias and its intervening marls 

 measure from 18 to 20 feet in thickness in Mr. Webb's quarry. 



In Mr. Fowler's quarry, about half a mile distant from the preceding, 

 the White Lias is more fully exposed ; it has here a thickness of 

 from 18 to 20 feefe and is underlaid by 18 inches of black shale, 

 beneath which is a coarse blue Lias limestone. The beds above the 

 White Lias are likewise here Avell exposed. 



