DIFFICULTIES AND OBJECTIONS 235 



structure, and also for minerals of different kinds 

 entering into their composition, and still presenting 

 precisely the same forms and structures. The third 

 is that first suggested, I think, by Jullien, and later 

 by Gregory and Lavis, that the forms are merely 

 banded alternations of calcite with silicious minerals 

 similar to those observed at the junction of igneous 

 rocks and limestones. To this it may be replied 

 that there is really only an apparent resemblance, 

 which, on careful examination, proves to be illusory ; 

 that it does not account for the canals and tubuli, 

 and that studies of such banded rocks from several 

 regions have been made by competent observers, 

 who have distinguished these from the Laurentian 

 Eozoon. The only remaining theory is that of the 

 filling of cavities by infiltration with serpentine. 

 This accords with the fact that such infiltration by 

 minerals akin to serpentine exists in fossils in later 

 rocks. It also accords with the known aqueous 

 origin of the serpentine nodules and bands, the 

 veins of fibrous serpentine, and the other minerals 

 found filling the cavities of Eozoon. Even the 

 pyroxene has been shown by Hunt to exist in the 

 Laurentian in veins of aqueous origin. The only 

 difficulty existing on this view is how a calcite 



