﻿66 Canadian Record of Science. 



We learn from the " Challenger " Reports that under 

 certain circumstances the presence of organic matter in 

 oceanic deposits causes an alkaline condition, tendin,sj to 

 the solution of silica and the formation of silicates. We 

 also learn that siliceous matter in a state of fine division 

 {e.g., volcanic dust) may afford material for the production 

 of hydrous silicates, either directly or indirectly through 

 the agency of organisms forming siliceous skeletons. The 

 "Challenger" Reports also show that the silicates known 

 under the name of glauconite, and thus deposited, contain 

 several bases to some extent interchancreable. Of these 

 the principal are aluminium, potash, and iron, though 

 magnesia is also present. Some older silicates injecting 

 fossils in the Palaeozoic rocks are less complicated, and 

 contain more masjnesia : and, as Hunt has shown, there is 

 nothing anomalous in the supposition that in the Lauren- 

 tian 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 Lime- 

 stone differs chemically from those supposed to be of 

 direct igneous origin, in its comj^arative 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 observa- 

 tions, 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 

 Chebogamoncp.2 



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

 tertiary example is silicate of iron and magnesia. Sec also Ho.skins on Glauconite, 

 Geol. Mag., July, 1895. 



2 Quart. Joiirn. Geol. Soc. 1864, p. 69, al.so 18Tt>, p. 48, ct svq., Memoir on Eozoon in 

 Peter Ile(li)atli Museum, 1888, p. 48 e< seq. 



