32 Principal J. W. Dawson on Eozoon canadense. 



fills large portions of tlie canal-system, and which in decalcified 

 specimens shows beautifully its characteristic cleavage and 

 lustre in the casts of the canals. 



4. The Origin of Serpentine. — " Serpentine," he says, " is 

 not an original, but a metamorphic rock." It may be answered 

 that on both geological and chemical grounds Hunt, Delesse, 

 Credner, and Giimbel arrive at a different conclusion, and 

 that in Silurian and otiier rocks serpentine itself and allied 

 silicates, like glauconite, iollyte, &c., occur as fillings of the 

 cavities of fossils. With regard to the £'o;2;oo/i-serpentine, 

 however, he believes that it is a product of the alteration of 

 olivine. He does not explicitly assert the occurrence of oli- 

 vine in the Canadian serpentines, but bases his assertion on 

 certain other specimens not Canadian, and on the appearance 

 of fissures and colours akin to those of olivine in some parts 

 of the Canadian specimens. In point of fact, as Dr. Hunt 

 has shown, olivine does occur in some Canadian ser})entines 

 of Huronian or Silurian age, but not, so far as ascertained 

 here, in those of the Laurentian system, in which the large 

 proportion of water indicated on analysis shows that this 

 anhydrous silicate cannot be present in any appreciable quan- 

 tity. Independently of this consideration, as olivine is a 

 mineral having a hardness of 6"5 to 7, or nearly twice that of 

 serpentine, if present in any of the numerous specimens sliced 

 and polished by Mr. Weston and myself, it could scarcely have 

 escaped our observation. In these circumstances I must regard 

 Hahn's determination from polariscope characters as quite un- 

 certain. Besides, I am familiar with the optical characters of 

 olivine, and know that serpentine often very closely resembles 

 it. Further, with reference to the alleged metamorphosis of 

 olivine into serpentine, it must be borne in mind that olivine 

 contains more of magnesia and other bases and less of silica 

 than serpentine, so that the mere addition of water could not 

 suffice to effect this change. As Dr. Hunt suggests to me, 

 the removal of a considerable part of the magnesia would be 

 necessary ; and this could scarcely have been effected except 

 by carbon dioxide, which would have acted by preference on 

 the surrounding limestone. Still further, as Scheerer long ago 

 objected, in the case of the Snarum serpentine, the expansion 

 consequent on the conversion of olivine into serpentine would 

 have broken up all the surrounding minerals. In the case of 

 the Canadian serpentine we have not only an absence of dis- 

 turbance, but the serpentine has actually become shrunken and 

 has had its fissures filled with chrysotile. 



But the conclusive facts with reference to the ordinary 

 aqueous origin of serpentine remain to be stated. In those 



