V 



Sir W. Daivson — The Animal Nature of Eozobn. 505 



silicates injecting fossils in the Palaeozoic rocks are less complicated, 

 and contain more magnesia; and, as Hunt has shown, there is 

 nothing anomalous in the supposition that in the Laurentian period 

 silicate of magnesium and iron may have acted in this capacity.^ 



It is true that serpentine is now usually regarded as a product of 

 the hydration of olivine and pyroxene ; still, even on this supposition, 

 it might be formed from the hydration of fine volcanic dust falling 

 into the sea. Hunt also has shown that the serpentine of the 

 Grenville Limestone differs chemically from those supposed to be of 

 direct igneous origin in its comparative freedom from iron oxide, in 

 its larger proportion of water, and in its lower specific gravity, 

 besides being a more pure silicate of magnesium. That it can be 

 deposited by water is shown by the chrysotile filling veins, and 

 by my own observations, published long ago, on the serpentine 

 replacing and filling cavities of Cambro-Silurian fossils at Melbourne 

 in Canada, and filling the cells of Silurian corals at Lake Chebo- 

 gamoug.^ 



The occurrence of pyroxene in the limestone, and filling some of 

 the chambers of Eozocin, may also be easily explained. Dr. Bouney 

 well remarks that it does not resemble any igneous rock known to 

 him, and it is quite certain from its mode of occurrence that it 

 cannot be directly igneous. Somewhat thick and continuous beds 

 of a coarser pyroxenite occur in some parts of the Grenville Series, 

 e.g. at Templeton, and I have described them as probably volcanic 

 ash-beds, while the large pyroxene crystals found in the veins of 

 apatite traversing these beds are probably of thermo-aqueous origin. 

 But the limited and irregular masses and concretions of white 

 pyroxene occurring in the limestones are of different texture and 

 colour, and more purely silicates of lime and magnesia. They may 

 have resulted from local showers of volcanic ashes drifted by 

 currents into hollows of the Eozoon reefs, and sufficiently fine to 

 fill the larger chambers of dead specimens, and when consolidated 

 to form a basis for the growth of new individuals. This is, I 

 think, the only supposition on which they can be explained, and it 

 would also explain the difficulty suggested by Dr. Bonney as to the 

 association of the pj'roxene with Eozoon. 



There seems, however, to be no good evidence that any portion 

 of the pyroxene has been changed into serpentine ; and it is evident 

 that if such a change had occurred after the consolidation of the 

 rock, serious chemical and mechanical difficulties would be involved, 

 whereas if volcanic debris, whether of the nature of olivine or 

 pyroxene, became hydrated while the rock was incoherent and in 

 process of formation, this would tend greatly to promote the in- 

 filtration with hydrous silicates of any fossils present in the mass. 



Assuming the serpentine and pyroxene to have been deposited as 



1 See Analyses of Glauconites, etc., by Dr. Hunt in "Dawn of Life," p. 126. 

 One tertiary example is silicate of iron and magnesia. See also Hoskins on 

 Glauconite, Geol. Mag., July 1895. 



^ Quart. Journ. Geol. Soc. 1864, p. 69, also 1879, p. 48 et seq., Memoir on 

 Eozoon in Peter Kedpath Museum, 1888, p. 48 et seq. 



