APPENDIX B 



A TABLE OF THE CHIEF GEOLOGICAL EPOCHS 



(The figures indicating the relative depth of the strata are 

 only roughly approximate. They are slightly adapted from Sir 

 Ray Lankester's book on Extinct Animals.) 



Period 



Typical Formation 



Characteristic fossils 



Archaean or 



Pre- Cambrian 



50,000 ft. 



Schists and me- 

 tamorphosed rocks, 

 probably represent- 

 ing stratified rocks 

 equal in thickness 

 to all subsequent 

 periods put together 



No trace of fossils, the re- 

 mains of which have all been 

 destroyed by alteration of rocks 



Cambrian 

 25,000 ft. 



Silurian 

 7,000ft. 



Devonian 

 5,000 ft. 



Carboniferous 

 and Permian 

 15,000 ft. 



Welsh slates, etc. 



Slates and shales 

 in Wales, etc. 



Ked Sandstones 

 of Devonshire, etc. 



Coal measures 

 of England, sand- 

 stones and lime- 

 stones 



Lingula, Trilobites, Nebaliid 

 Crustacea, various Molluscs 



Arachnids, Ostracoderm 

 fishes 



Eurypterids, Elasmobranch 

 and Bony fishes (Actinopterygii 

 and Dipnoi) 



Trilobites dying out. Deca- 

 pod Crustacea, Anaspids, Insects, 

 Stegocephalian Amphibia. First 

 appearance of terrestrial verte- 

 brates 



