GEOLOGY OF THE BKISTOL COAL-FIELD. 



Orthis elegantula 



basalis (Dalm.) 



Strophomena Waltoni (Dav.) 

 depressa 

 englypha 



Corals and Encrinites 



267 



Fig. 6. — Tortworth Anticlinal, 

 d c 



a Upper Silurian. — b Devonian. — c Carboniferous. — t? Trias. 



The Orthis basalis and Crania Siluriana are fossils as yet only 

 found in the Talfield district. Another section may be examined 

 near Avening. Here the Wenlock coral bed is actually lifted up 

 by an outburst of lava, with the corals altered by the heat. 



III. TJie Ludlow Shales. 



These, although so extensively extended over the country, are 

 not well placed for the collection of fossils. For this reason no 

 satisfactory list of fossils can be made. 



THE DEYONIAN. 



The Devonian, or Old Eed Sandstone, in the neighbourhood of 

 Bristol, comprises Sandstones, Shales, and Conglomerates, usually 

 strongly coloured with Ferric oxide, but sometimes purplish 

 yellow or green, from the presence of Ferrous oxide. The 

 Devonian character differs from the Silurian bedp, which are very 

 argillaceous and calcareous. 



As shewn in Fig. 7, the Old Ked Sandstone underlies the 



