356 Prof. Keilhau on the Formation of 



very occiirrence of the marble, in place of compact limestone, 

 in contact with the rocks regarded as pyrogenic ! As, indeed, 

 uncrystalline limestone deposits, similarly constituted to those 

 which exhibit the conversion into marble in the vicinity of 

 these other rocks, present the same phenomena of conversion 

 in cases where heat has undoubtedly not produced the change 

 (as in the instances mentioned at first, p. 10, &c.), it follows, 

 that there is no existing necessity for our being obliged to re- 

 gard the contact-marble as a product of heat. Such a mode of 

 formation would only become probable^ if the said marble were 

 without exception found in contact with undoubted pyrogenic 

 rocks. As, therefore, this is not the fact, the cautious geolo- 

 gist must find himself far removed from being able positively 

 to declare, that contact-marble receives a full explanation from 

 Hall's experiment. 



It is frequently asserted that the ordinary compact lime- 

 stone, presenting a crystalline structure at its contact with the 

 bounding rock, is no longer stratified where it has become 

 crystalline, and that there the fossils, which elsewhere are dis- 

 tinct, have become obscure, or have even completely disap- 

 peared. This is certainly true in very many instances^ and 

 both phenomena are also very natural. As, however, these 

 phenomena must exist in such positions according to the pre- 

 vailing theory, because that theory presupposes that the lime- 

 stone was at least rendered soft by the heat in order to be- 

 come crystalline, a deficiency is apparent, inasmuch as it is by 

 no means the fact, that such phenomena occur, without excep- 

 tion, in contact-marble. In the district of Christiania, fossils, 

 with perfectly distinct outlines, are found in marble next the 

 granite.* Here the mass of limestone evidently did not lose 

 its solid condition during its conversion into marble. The ne- 

 cessity is thus removed, as far as I can judge, of presupposing 

 an excessive temperature ; and thus the process of conversion 

 is placed in the same class with those crystallizations, so com- 

 pletely proved by observation, of solid amorphous bodies, where 



* The Museum of the University of Christiania possesses an extremely beau- 

 tiful specimen of this description, in which the Catenipora labyrinthica is fully b.% 

 distinct as in the completely uncrj'stalline limestone of the same district. 



