390 PROCEEDINGS OE THE GEOLOGICAL SOCIETY. [Feb. 29, 



tion of this zone of life, I shall adhere to it on the present occasion, — 

 premising, however, that Ammonites are very rare in the lower beds, 

 although abundant in the upper ; and that Ostrea? are abundant 

 below, but rare above, whilst Saurian remains are found throughout 

 the entire series. 



Somersetshire. — The best sections of the zone of Ammonites pla- 

 norbis are those afforded by the extensive quarries at Street, in 

 Somerset, and at Binton and Wilmcote, in Warwickshire. I purpose 

 to give a detailed description of the most typical section in each 

 county. In both, the strata are nearly horizontal and undisturbed, 

 and therefore admit of accurate measurement. 



The following section of Mr. Cree's quarry at Street I have com- 

 pared with the sections afforded by the quarries of Messrs. Seymour, 

 Underwood, and Talbot in the same parish ; and find that the varia- 

 tion in all these sections is so inconsiderable that any one may be 

 said to represent the others, both as regards the sequence of the beds 

 and the fossils they contain. 



Section of the Zone of Ammonites planorbis at Street, Somerset. 



Lithology. Organic Remains ; and the Local 



No. ft. in. Names of Beds. 



1. Light-coloured marly clay ... 3 " Top bed." Saurian bones and Am- 



ononites planorbis. 



2. Light-coloured Lias limestone 9 Ammonites planorbis in moulds. 



3. Yellowish laminated shale, Ichthyosaurus intermedins, Ammonites 



splitting up into thin layers 3 planorbis, Lima punctata, and Isa- 



strcsa Murchisoni. 



4. Light-coloured shaly lime- Ammonites planorbis, compressed. 



stone 4 



5. Hard grey limestone 7 "Building-stone." Ammonites plan- 



orbis, on the top of the bed, Lima 

 punctata and Lima gigantea. 



6. Dark-grey shale 3 Ammonites planorbis, and muricated 



spines of Ciclaris. 



7. Dark-grey limestone 6 "Corn-sized building-stone." Spines 



of Cidaris and bones of Ichthyo- 

 saurus tenuirostris. 



8. Dark laminated shale 4 Ostrea liassica. 



9. Dark-grey limestone 5 "Five-inch building-stone." Ostrea 



liassica. 



10. Dark shale 3 Ostrea liassica. 



11. Dark-grey limestone 6 " Six-inch building-stone." Cardinia 



crassiuscula, Lima punctata, and 

 Ostrea liassica. 



12. Dark shale 6 



13. Greyish hard limestone, con- " The "White stone." Best paving- 



sisting of two 4-inch beds ... 8 bed. Fossils rare ; Ostrea liassica 



and Modiola minima. 



14. Hard dark marl 9 " Saurian bed." Many Saurians have 



been obtained here. Ichthyosaurus 

 intermedins and Plesiosaurus Haw- 

 kinsii (British Museum). Jaws of 

 Saurians and Fishes. 



15. Greyish fine-grained limestone 3 "The Cream-bed." Fine-grained 



paving-stone. Ostrea and Modiola. 



1 6. Brownish limestone 4 "Bed Liver.' ' Paving-stone. Few 



fossils. 



