FOSSILS OF OLD RED SANDSTONE. 57 



nounced to us at a lower point in that formation. 

 But how far it is likely that our information is to 

 rest at this point the reader may judge, when he 

 hears of M. Agassiz announcing, within the last 

 few months, that, though acquainted with seven- 

 teen hundred species of fossil fishes he regards 

 the history of the class as so far from complete, 

 that the number of species successively entombed 

 in the crust of the globe might be estimated at 

 thirty thousand, without any chance of approach- 

 ing the truth !* If such be the case, we may surely 

 expect to hear of other fishes prior to or contem- 

 porary with the cestraceon, showing that, humble 

 as that animal was, it is not to be regarded as the 

 initial of its class.f But even although simpler 



olites which succeed in that enormous formation, the Old Red 

 Sandstone." — Murchison^a Address to the Geological Society, Fe- 

 bruary, 1842. 



* Review of Professor Pictet's Traite Elementmre de Palseon- 

 tologie, translated in Jameson's Journal from the Bibliotheqae 

 Universelle de Geneve, No. 112, 1S45. 



f Such shifts are of frequent occurrence in geology. Insects, 

 formerly found first in the oolitic formation are now taken back 

 to the carboniferous. Birds are now inferred from foot-tracks in 

 the New Red Sandstone, their first place formerly being in the 

 oolite. We have mammifers in the oolite, which a few years 

 ago, were believed not to occur before the tertiarj-. None of these 

 shifts, however, in the least interfere with the general fact of the 

 advance from the lower to the higher classes of animals. 

 d 3 



