208 SAUROID FISHES. 



yet been found that is common to any two great geological 

 formations ; or living in our present seas.* 



One important geological result has already attended the 

 researches of M. Agassiz, viz. that the age and place of 

 several formations hitherto unexplained by any other cha- 

 racter, have been made clear by a knowledge of the fossil 

 Fishes which they contain.f 



Sauroid Fishes in the Order Ganoid. 



The voracious family of Sauroid, or Lizard-like Fishes, 

 first claims our attention, and is highly important in the 

 physiological consideration of the history of Fishes, as it 



* The nodules of clay stone on the coast of Greenland, containina^ fishes 

 of a species now living in the adjacent seas, (Mallotus Villosus) are probably 

 modern concretions. 



f Thus the slate of Engl, in the canton of Claris, in Switzerland, has long 

 been one of tiie most celebrated, and least understood localities of fossil Fishes 

 in Europe, and the mineral character of this slate had till lately caused it to 

 be referred to the early period of the Transition series, M. Agassiz has 

 found that among its numerous fisiies, there is not one belonging to a single 

 genus, that occurs in any formation older than the Cretaceous series ; but 

 that many of them agree with fossil species found in Bohemia, in the lower 

 Cretaceous formation, or Planer kalk ; hence he infers that the Claris slate 

 is an altered condition of an argillaceous depositc, subordinate to the great 

 Cretaceous formations of other parts of Europe, probably of the Gault. 



Another example of the value of Ichthyology, in illustration of Geology, 

 occurs in the fact, that as the fossil Fishes of the VVealden estuary forma- 

 tion are referable to genera that characterize the strata of the Oolitic series, 

 the Wealden deposiles are hereby connected with the Oolitic period that 

 preceded their commencement, and arc separated from the Cretaceous for- 

 mations that followed their termination. A change in the condition of the 

 higher orders of the inhabitants of the waters seems to have accompanied 

 tlie changes that occurred in the genera and species of inferior animals at 

 the commencement of the Cretaceous formations. 



A third example occurs, in the fact that M. Agassiz has, by resemblances 

 in the character of their fossil Fishes, identified the hitiierto unknown pe- 

 riods of the fresh-water deposites of Oeningen, and of Aix in Provence, with 

 that of the Molasse of Switzerland. 



