74 PROC. COTTESWOLD CLUB vol. xiii. (2) 



As we follow the succession of life downwards through 

 Tertiary, Mesozoic. and Palaeozoic formations, we find the 

 higher types gradually disappearing. Man we lose almost 

 at the start. He may be found below the Post-Pleiocene 

 rocks, but we have not identified him yet with certainty 

 in older strata. A corresponding qualification will apply 

 to the first appearance of all animals and plants. We 

 know where we first find them, we do not know how 

 much older they may really be. The Mammalia dis- 

 appear in the Upper Trias, birds in the Jurassic, reptiles 

 in the Permian, Amphibia in the Carboniferous, and fishes 

 in the Ordovician. The Vertebrata had therefore been 

 evolved at least as early as the Ordovician, and it is not 

 improbable that they commenced their existence as simple 

 worm-like fishes, even in Cambrian times. 



In the Cambrian rocks, from the top right down to the 

 base, we find an abundant fauna. Even in the lowest 

 Cambrian strata we have proof that nearly all the chief 

 types of life below the Vertebrata had l)een evolved. 

 We can detect sponges, Crustacea, Brachioj)oda, Gastero- 

 poda, and conical shells which were formerly thought to 

 be Pteropoda, but are now regarded as the ancestors of 

 the Kephalopoda, the highest of all the molluscs. These 

 are but the refics of worlds of life that peopled the earliest 

 Cambrian seas, for the occurrence of these animals 

 implies the co-existence of numerous types which had no 

 bone, or shell, or crust to perpetuate their memory. 



But in the Pre-Cambrian rocks the traces of the life of 

 the globe are meagre in the extreme. The abundance of 

 the Cambrian period suddenly sinks almost to zero. It 

 is as if, in tracing back the history of England, we passed 

 in a moment from the varied life of the Elizabethan epoch 

 to the poverty and emptiness of the Age of Bronze. 



Yet we are sure that the seas of the Pre-Cambrian 

 ages were teeming with living creatures. We believe it 



