238 OUR COMMON BRITISH FOSSILS. 



world-wide character — many of the same species dis- 

 tinguish Australian and American limestones and 

 shales which are characteristic of British rocks. Alto- 

 gether this is a most interesting series of animal 

 forms, and one which has played no small share in 

 the formation of the stratified rocks of the earth's 

 crust — living on through long periods of geological 

 time ; silent witnesses of those great world-throes 

 and world-changes, each appearing at the time 

 destructive, but all of which were combined to make 

 our world such as we find it to-day. 



