^^ Microyeological Investigation uf Fiozoow caiuidcnse." 419 



by Dr. Hahii as to the mineralized condition of the Eozoic 

 Ophicalcite merely bears upon its i^resent metamorj^liic condi- 

 tion, and proves nothing in regard to its original character ; 

 as to which, as in all similar cases, our conclusions must be 

 drawn from the examination of specimens which show the 

 least evidence of metamorphism. Suppose that there were 

 found, somewhere in the Carboniferous series, an extensive 

 calcareous deposit, including a number of masses whose general 

 character seemed Vegetable, though not conforming to any 

 known type ; and suppose, further, that on an examination of 

 their internal substance, a large proportion of them proved 

 to consist (as often happens) of calcspar, with quartz or other 

 crystalline minerals scattered through it ; whilst others, again, 

 exhibited obscure and uncharacteristic traces of woody or 

 cellular structure ; — would not the discovery of a single well- 

 preserved fragment, showing an unmistakable vegetable tissue, 

 be regarded by every Palteontologist as adequate evidence that 

 even the completely mineralized specimens were true fossils, 

 not mere pseudomorphs ? 



3. It is affirmed by Dr. Hahn (p. 274) that " for every part 

 of a rock the jyi'esumption is in favour of mere rock- forma- 

 tion," He would seem, therefore, entirely unaware of the 

 weight of evidence which has been gradually leading Geolo- 

 gists of the largest knowledge and ripest judgment to the con- 

 clusion that, in the case of calcareous rocks, the presumption 

 is all the other wag. No one, of course, doubts that inorganic 

 Limestones may have been formed in old times, as they are 

 being formed now, by simple deposit from waters holding an 

 excess of carbonate of Ynne in solution. But, on the other 

 hand, the resemblance of the organic calcareous deposits at 

 present in process of formation upon the sea-bed, to the various 

 calcareous strata of former epochs, taken in connexion with 

 the knowledge we now possess in regard to the modes in which 

 the traces of original organic structure may be obliterated by 

 various forms of metamorphic action, afford a presumption in 

 favour of the organic origin of any Calcareous rock-formation ; 

 the strength of which presumption is somewhat in the jn-oportion 

 of the extent which the Olobigerina-deTposit of our great Oceans, 

 and the vast accumulation of the debris of Coral within the 

 Barrier-reef of New Holland, bear to the local Travertine 

 limestones of Italy — being almost as strong, in fact, as the 

 presumption that a bed of Graphite or Anthracite, showing 

 no trace of a Coal-plant, represents an antecedent Vegetation. 

 On Dr. Hahu's method of reasoning, the statuary-marble of 

 Carrara, which is a rock of a finely crystalline texture, like 

 that of loaf-sugar, showing little or no trace of beddim;-, and 



