158 FIELD GEOLOGY. 



of rocks, and is almost always found wherever the group 

 extends, we may speak of these as the characteristic 

 species of the group. It occasionally happens that the 

 fossils of such a group are so nearly allied biologically 

 that naturalists form them into a genus, or into one or 

 two genera, which may then be spoken of as equally 

 characteristic."* 



A list of the more common characteristic fossils has 

 been compiled from various sources, f and is given below, 

 arranged not in the order of succession of the rock for- 

 mations, but alphabetically, so that if a fossil be known 

 the approximate (if not exact) geological position of the 

 rock from which it has been derived can readily be de- 

 termined. 



* " Manual of Geology," Jukes and Geikie, p. 502. 

 t Murchison's Siluria. 



Lyell's Manual, Students' Elements, &c. 



Jukes and Geikie's Manual. 



Buckland's Bridgewater Treatise. 



Man te IPs Medals, Wonders of Geology, &c. 



Phillips' Manual, Palceozoic Fossils, &c. 



M'Coy, Palceozoic Fossils. 



Portlock, Geological Reports. 



Owen, Palaeontology. 



Wright, Brit. Foss. Echinodermata. 



King, Permian Fossils. 



Geological Magazine. 



Tabular View of British Fossils stratigraphically arranged. 



Publications of H. M. Geological Survey. 

 the Geological Society. 



Palceontographical Society. 



