330 ON THE DEPOSITS CALLED TERTIARY 



water lakes. The process of naturalization, conducted 

 under my own directions, has moreover shown that 

 the Turbot, sole, plaice, mullet, smelt, atherine, horse 

 mackerel, pollock, loach, basse, rock fish, whiting 

 pout, rockling, prawn, crab, and stickleback, 'in ay be 

 habituated without difficulty to fresh water ; while all 

 those which have hitherto had time enough, have 

 bred and propagated. 



Such examples render it probable that most, if not 

 all fishes, are indifferent to the quality of the water, 

 provided they can find food : and when it is considered 

 how many changes the surface of the earth may have 

 undergone, it is evident that no judgment respecting 

 the nature of a deposit, can be derived from a pre- 

 vious decision respecting the imagined habits of fishes 

 as to the quality of the water in which they may have 

 resided. 



What is not less important in a geological view, 

 every species on which this trial has yet been made, 

 suffers alternate changes from fresh water to salt with- 

 out inconvenience ; having been retained in a pond 

 where these alterations take place. It is easy to see 

 how these facts must affect our decisions respecting 

 the nature of marine and fresh water deposits as far as 

 that is to be determined by the remains of fishes. 

 I need here only add, that as far as the question of 

 respiration is concerned, there ought to be no difficulty 

 in the change from salt water to fresh 5 since the ad- 

 hesion of the oxygen is less strong to the latter than 

 to the former. 



But, from the fact that the Pike and the Cyprini 

 prefer the Caspian when they might remain in the 

 Wolga, it is not improbable that many or all fresh 

 water fish might also endure the sea permanently, as 

 the Salmon and others do, interruptedly. And though, 



