THE STORY OF THE EARTH. 



and southward through Lincolnshire into Oxford- 

 shire The Middle Lias is about 250 feet thick 

 on the south coast; and 140 feet thick on the 

 Yorkshire coast. Near Cheltenham the lower 

 part includes some grey sand, and is about 150 

 feet thick. The difference from the Lower Lias 

 m fossils is Chiefly in the species of Ammonites 



and Belemnites. Some 



< -^~'^— ». of its upper beds are 



Uftf?^* >Si known as the Helem- 



nite beds, from the 



iJBliSP 1 * abundance of this fos- 



JK\*^~ ,. >, sil. In these beds 



■BHr fishes 



^^^S^ ^ & tnc genus Ophioderma 



^^^B ' mSF^ are found, both on 



Fig 2 i.-Cardinia Listen: Lias. the Yorkshire coast, 



and near ( narmouth. 

 The Upper Lias is usually very thin on the 

 Coast of Dorsetshire, about 70 feet, including the 

 associated sands near Charmouth. But it thick- 

 ens northward to 300 feet near Cheltenham, and 

 400 feet further north in Bredon Hill; maintain- 

 ing a thickness of 300 feet m Leicestershire, but 

 thinning in Lincolnshire and Yorkshire to 200 

 feet or" less. On tin- Yorkshire coast it is often 

 known as alum shale, alum having formerly 1 

 obtained from the cliffs and manufactured from 



the -hale. Near the base there are beds o\ jet. 



m which the rings of growth of the coniferous 

 es out <>f which it was formed, may occasion- 

 ally be observed. In the Upper Lias at limn 

 many [chthyosaurs, Plesiosaurs, and crocodile 

 group Teleosauria are met with. A little 

 her up, in the zone of the Ammonias t 



Ammonites UfrOfU near Whitby, the same 



