36 Principal J. W. Dawson on Eozoon canadense. 



confound Avith the veins of chrysotile or fibrous serpentine 

 which traverse the specimens, or with fringes of fibrous crystals 

 at the margins of the grains and plates of serpentme i et 1 

 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 Inoceramus. 

 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 ot the 

 masses of Eozoon, and passing through the containing rocks. 

 I am not, however, surprised at this confusion, as I have often 

 had occasion to observe the similarity at first sight of thmgs 

 so unlike as sections of crystals of mica, ot veins of satm-spar 

 and of shells of mollusks, crustaceans, and Nuramulites. J3ut 

 the existence of the chrysotile veins themselves orof the sup- 

 posed fringes of serpentine crystals is almost as inexplicable 

 on Hahn's theory as that of the organic cell-wall itselt.^ _ 



Supposed Pr^udices of Zoologists. -^o\h at the beginning 

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

 possessions of zoologists, and their inexperience m examining 

 mineral substances, and even hints at their being likely to 

 mistake the crystals in the pitchstone of Arran lor orgamc 

 forms He forgets that there are now many observers tamiliar 

 mot onlv 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 oiEozoon, I may merely mention tne 

 several kinds of mineral or organic structures which 1 have 

 found to be capable of misleading unpractised observei-s, and 

 all of which have actually been compared carefu ly with this 

 ancient fossil. They may be arranged under the following 

 heads •— (1) Dendritic crystallizations, as those ot_ oxides ot 

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

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

 certain felspars. (2) Coralloidal and vermicular crystalliza- 

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

 (3) Radiating and fibrous crystallizations, as those oi satm- 

 spar of oolitic grains and other concretions, and of tremohte 

 in limestones, aSd 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 whidi have 

 been aff-ected with shrinkage, which has permitted their fissures 

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

 segregation-veins, such as occur in masses of heterogeneous 

 minei al matter : these fissure-vems are often beautifully deve- 



