236 



OUR COMMON BRITISH FOSSILS. 



which accumulated on the ancient Silurian sea- 

 bed. The original lime of the shells has in all these 

 instances been dissolved away by the action of perco- 

 lating water. 



The Upper Silurian rocks, limestones, and shales 

 are perhaps the best hunting-grounds for fossil 

 Brachiopoda. More than a hundred species are found 



Fig. 218. — Terebratula 

 deformis. 



Fig. 219. — Tereh'atula lyra. 



P'ig. 220. — Terebratula dorsata. 

 (showing interior). 



in them, and there is not a single locality where these 

 rocks are quarried (that I know of) where fossil 

 Brachiopoda cannot be obtained. Some districts are 

 especially noted for them — the Wren's Nest, near 

 Dudley; Aymestry; Woolhope; theMalverns ; Girvan, 

 in Ayrshire, etc. They are not less common in the 

 Devonian and Carboniferous limestones as regards 



