64 PEOCEEDINGS OF THE GEOLOGICAL SOCIETY. 



their proper interpretation. Skeletal elements which were originall)^ 

 siliceous are now represented by pseudomorphs in calcite, and vice 

 versa. Characteristic structures in bones, shells, or wood may be 

 wholly obliterated, and mineral structures of a strangely deceptive 

 kind may be developed in their place. The curious story of Eozoon 

 canadense and its supposed allies is surely a sufficient justification 

 for the existence of palaeontologists — that is, of specialists trained 

 equally in the interpretation of biological and petrological structures. 

 Dr. Sorby has shown that whole families of Mollusca may disappear 

 from a fauna because of the unstable condition of the calcic car- 

 bonate which composes their shells, and his conclusions have been 

 confirmed by Mr. Kendall. 



Professor Sollas has similarly shown that the absence of the Por- 

 cellanous types of the Eoraminifera from the palaeozoic rocks may be 

 due not to their non-existence when those rocks were formed, but 

 to the fact of their shells being composed of the unstable Aragonite. 



Such facts as these must convince any unprejudiced person of the 

 absolute necessity to the naturalist, who attempts to study extinct 

 forms, of an acquaintance with the nature of the mineral changes 

 which organic remains undergo. In his interesting memoir upon 

 those curious and enigmatical fossils, the E-eceptaculitidae, Dr. 

 Hinde has admirably illustrated the advantages of this combination 

 of Biological and Petrographical study. 



In this connexion I cannot avoid alluding to a very prevalent 

 and, as I cannot help thinking, very erroneous notion, that an 

 intermingled zoological and palseontological collection, however in- 

 convenient, would certainly be very instructive. Against this view 

 I off'er the strongest protest, for I believe that the mistakes which 

 would arise from the examination of such a collection would far 

 outweigh any instruction to be derived from it. 



To begin with, I fail to see what useful lesson would be taught 

 by burying the collection of the lizards, snakes, tortoises, and 

 crocodiles of the present day, among the vast slabs containing the 

 relics of Eeptilia which have lived in periods ranging from the 

 Permian to the Pliocene. Nor is it apparent to me why the 

 precious remains of Archoeopteryoc should be hidden away among a 

 wilderness of bird-skins. 



But my most serious objection arises from the conviction that any 

 arrangement which would lead to the idea that even the richest 

 collection of fossils is in any way commensurable with the assem- 

 blages of specimens that in our museums represent the existing 



