70 PEOCEEDINGS OF THE GEOLOGHCAL SOCIETY. [,NoV. 23, 



eates which now constitute pyroxene, serpentine, and loganite were 

 directly deposited in waters in the midst of which the Eozoon was 

 still growing or had only recently perished, and that these silicates 

 penetrated, enclosed, and preserved the calcareons structure precisely 

 as carbonate of lime might have done. The association of the sili- 

 cates with the Eozoon is only accidental, and large quantities of 

 them, deposited at the same time, include no organic remains. Thus, 

 for example, there are found associated with the Eozoon-limestones 

 of Grenville massive layers and concretions of pure serpentine ; and 

 a serpentine from Burgess has already been mentioned as containing 

 only small broken fragments of the fossil. In like manner large 

 masses of white pyroxene, often surrounded by serpentine, both of 

 which are destitute of traces of organic structure, are found in the 

 limestone at the Calumet. In some cases, however, the crystalliza- 

 tion of the pyroxene has given rise to considerable cleavage-planes, 

 and has thus obliterated the organic structure from masses which, 

 judging from portions visible here and there, appear to have been at one 

 time penetrated by the calcareous plates of Eozoon. Small irregular 

 veins of crystalline calcite, and of serpentine, are found to traverse* 

 such pyroxenic masses in the Eozoon-Hmestone of Grenville. 



As already mentioned in Sir W. E. Logan's description, it appears 

 that great beds of the Laurentian limestones are composed of the 

 ruins of the Eozoon. These rocks, which are white, crystalline, and 

 mingled with pale-green serpentine, are similar in aspect to many 

 of the so-called primary limestones of other regions. In most cases 

 the limestones are non-magnesian, but one of them from Grenville 

 was found to be dolomit'c. The accompanying strata often present 

 finely crystallized pyroxene, hornblende, phlogop^'.te, apatite, and 

 other minerals. These observations bring the formation of siliceous 

 minerals face to face with life, and show that their generation was 

 not incompatible with the contemporaneous existence and the pre- 

 servation of organic forms. They confirm, moreover, the view which 

 I some years since put forward, that these silicated minerals have 

 been formed, not by subsequent metamorphism in deeply buried 

 sediments, but by reactions going on at the earth's surface t. In 

 support of this view, I have elsewhere referred to the deposition of 

 silicates of Hme, magnesia, and iron from natural waters, to the great 

 beds of sepiolite in the imaltered Tertiary strata of Europe, to the 

 contemporaneous formation of neolite (an alumino-magnesian silicate 

 related to loganite and chlorite in composition), and to glauconite, 

 which occurs not only in Secondary, Tertiary, and Eecent deposits, but 

 also, as I have shown, in Lower Silurian strata J. This hydrous 



* Recent examinations have shown that some of these masses encrusted with 

 Eozoon, replaced by serpentine, consist of crystalhne pyrallohte (rensselaerite), 

 which seems, hke the other sihcateSjto have replaced the organic matter of the 

 Khizopod. Fm'ther examinations, aided by the microscope, are however needed 

 to determine with certainty the relations of the Eozoon to these masses of pyral- 

 lohte. 



t Amer. Journ. Science, 2nd ser. vol. xxix. p. 284 ; vol. xxxii. p. 286. Greo- 

 logy of Canada, p. 577. 



X Amer. Journ. Science, 2nd ser. vol. xxxiii. p. 277. Geology of Canada, p. 487. 



