198 TBE DAWN OP LIFE, 



including a perfect canal system preserved in malscolite. 

 With reference to this, as spinels of large size occur in veins 

 in the Laurentian rocks, I am not prepared to say that it is 

 absolutely impossible that fragments of limestone containing 

 Eozoon may not be occasionally associated with them in their 

 matrix. I confess, however, that until I can examine such 

 specimens, which I have not yet met with, I cannot, after my 

 experience of the tendencies of Messrs. Rowney and King to 

 confound other forms with those of Eozoon, accept their 

 determinations in a matter so critical and in a case so 

 unlikely.* 



If all specimens of Eozoon were of the acervuline character, 

 the comparison of the chamber-casts with concretionary 

 granules might have some plausibility. But it is to be ob- 

 served that the laminated arrangement is the typical one ; and 

 the study of the larger specimens, cut under the direction of 

 Sir W. E. Logan, shows that these laminated forms must have 

 grown on certain strata-planes before the deposition of the 

 overlying beds, and that the beds are, in part, composed of the 

 broken fragments of similar laminated structures. Further, 

 much of the apparently acervuline Eozoon rock is composed of 

 such broken fragments, the interstices between which should 

 not be confounded with the chambers : while the fact that the 

 serpentine fills such interstices as well as the chambers shows 

 that its arrangement is not concretionary. Again, these 

 chambers are filled in different specimens with serpentine, 

 pyroxene, loganite, calcareous spar, chondrodite, or even with 

 arenaceous limestone. It is also to be observed that the examin- 

 ation of a number of limestones, other than Canadian, by 

 Messrs. King and Eowney, has obliged them to admit that the 

 laminated forms in combination with the canal- system are 

 " essentially Canadian," and that the only instances of struc- 

 tures clearly resembling the Canadian specimens are afforded 



* I have since ascertained that Laurentian limestone fotmd at 

 Amity, New York, and containing spinels, does hold fragments of the 

 intermediate skeleton of Eozoon. The limestone may have been 

 originally a mass of fragments of this kind with the aluminous and 

 magnesian material of the spinel in their interstices. 



