LIFE ON THE EARTH. 115 



TERRESTRIAL LIFE. 



The information afforded by freshwater deposits, 

 and the effects of freshwater currents flowing into 

 the sea, is strongly reflected in the history of the 

 ancient land. As the stream flows down from its 

 parent mountains, gathering air and penetrated by 

 light, it soon begins to swarm with infusoria, feeding 

 among the immersed and marginal vegetation; Pla- 

 norbes, Limnseadse, Cycladse, appear in its sparkling 

 or quiescent water; Gammarinso and Daphnise, Insects 

 and Argyronetse, furnish delicate diet to the watch- 

 ful Trout ; and thus race follows race, till finally Uni- 

 onidse prevail and occupy the bed of the current as it 

 slowly winds toward the estuary, which, itself almost 

 deserted, divides the fluviatile from the oceanic 

 worlds of life. 



When in the Coal-formation we find an abun- 

 dance of Unionidse, often buried in colonies as they 

 lived, in layers of fine sediment, alternating with 

 Coal Strata, accumulated towards the margin of the 

 sea, we may easily connect in imagination this 

 marshy savannah with rivers descending from the 

 interior, and suppose on their banks many races of 

 animals whose remains, if rare., may nevertheless 

 occur to diligent search on favourable occasions. 



By such scrupulous attention to the contents of 

 Ironstone nodules at Coalbrook Dale Mr Anstice 



12 



