36 Principal J. W. Dawson on Eozoon canadense. 



confound with the veins of chrj'sotilc or fibrous sei-pentine 

 which traverse the specimens, or with fringes of fibrous crystals 

 at the margins of the grains and plates of serpentine. Yet I 

 can testify that the difference between the cell-wall, when 

 properly preserved, and any vein of crystalline mineral is as 

 great as between the tubulated shell of a Brachiopod or a 

 worm and the prismatic shell of a Pinna or hioceranius. 

 Further, under polarized light the chrysotile veins have a 

 brilliancy altogether wanting in the proper wall ; and I have 

 shown that the chrysotile is of subsequent origin to the cell- 

 wall, and forms true veins traversing all the structures of the 

 masses o^ Eozoon, and passing through the containing rocks. 

 I am not, however, sm-prised at this confusion, as I have often 

 had occasion to observe the similarity at first sight of things 

 80 unlike as sections of crystals of mica, of veins of satin-spai*, 

 and of shells of mollusks, crustaceans, and Nummulites. But 

 the existence of the chrysotile veins themselves or of the sup- 

 posed fringes of serpentine crystals is almost as inexplicable 

 on Hahn's theory as that of the organic cell-wall itself. 



Supposed Prejudices of Zoologists. — Both at the beginning 

 and end of his paper Halm takes occasion to refer to the pre- 

 possessions of zoologists, and their inexperience in examining 

 mineral substances, and even hints at their being likely to 

 mistake the ciystals in the pitchstone of Arran for organic 

 forms. He forgets that there are now many observers familiar 

 not only with the structures of all kinds of animal and vege- 

 table fossils, but with mineral substances as well. In the case 

 of the canals and tubuli of Eozoon, I may merely mention tlie 

 several kinds of mineral or organic structures which I have 

 found to be capable of misleading impractised observers, and 

 all of which have actually been compared carefully with this 

 ancient fossil. They may be aiTanged under the following 

 heads : — (1) Dendritic crystallizations, as those of oxides of 

 iron and manganese in moss-agates and in calcite &c., of 

 native copper and silver in calcite veinstones, and of mica in 

 certain felspars. (2) Coralloidal and vermicular crystalliza- 

 tions, as those of aragonite. Dolomite, and of vermicular mica. 

 (3) Radiating and fibrous ciystallizations, as those of satin- 

 spar, of oolitic grains and other concretions, and of tremolite 

 in limestones, and the very similar structures which are found 

 in the shells of Inocerami and other mollusks. (4) Micro- 

 scopic cracks, such as occur in mineral substances which have 

 been affected with shrinkage, which has peimitted their fissures 

 to be filled with different substances of later origin ; or minute 

 segregation-veins, such as occur in masses of lieterogeneous 

 mineral matter : these fissure-veins are often beautifully deve^ 



