298 Professor Agassiz on 



Having made these general remarks, let me now proceed to 

 a few criticisms or details. M. Pictet very judiciously rejects 

 the opinion of M. De Blainville, who imagines that he has 

 proved that the fossil bears of caverns are identical Avith our 

 recent species ; but I think that M. Pictet goes too far when 

 he affirms that all the best investigations of careful zoologists 

 have shewn that the fossils are different in each formation. 

 In representing the question in this manner, he forgets that 

 M. Deshayes, who, of all modern conchologists, is the observer 

 most entitled to our confidence, asserts that a very large num- 

 ber of the tertiary species are identical in the different forma- 

 tions of that great epoch, and that eminent geologists have 

 adopted the determinate proportions of tertiary species which 

 are identical with living ones, as a distinctive character of the 

 different tertiary formations : he also forgets that Ehrenberg, 

 whose splendid investigations have thrown so much light on 

 the mode of formation of the sedimentary strata, maintains the 

 identity of hundreds of species occurring in the chalk, in the 

 tertiary series, and at the present day. Let it not be imagined 

 that I am opposed to M. Pictet's view of the subject ; for, on 

 the contrarv, I am, like him, convinced that these identifica- 

 tious are inaccurate : but it is to prove this at some future 

 time that our investigations ought to tend ; for, far from hav- 

 ing received general assent, this mode of viewing the question 

 has hitherto been adopted by M. D'Orbiguy alone, who, in his 

 classical work on French Palaeontology, was the first to prove 

 that each of the members of the cretaceous series has a pecu- 

 liar fauna, just as I have asserted to be the case in regard to 

 the Jurassic and tertiary formations. 



In speaking of fossil seals, M. Pictet forgets to quote the 

 finest known example, viz., a fragment of a jaw figured by 

 Scilla in his work De Corporibus JSFarinis Lapidescenlibus, 

 1752, plate xii., fig. 1. He ought also to have been able to 

 ascertain, from the letters of H. von Meyer, published in 

 Leonhard and Brcnn's Journal (letters containing important 

 palaeontological information, and which have been generally ne- 

 glected in this volume), that the Ancema Oeninc/ensis of Cuvier 

 is a true Lagomys, — a fact which I have ascertained by the 

 inspection of the original specimen figured in the Becherches 

 sur les Ossements Fossiles. Von Meyer's letters would like- 



