1865.] HUNT — MINERALOGY OF EOZOON. 125 



of serpentine, are found to traverse* such pyroxene-masses in the 

 Eozoon-lirnestone of Grenville. 



As already mentioned in Sir TV. E. Logan's description, it ap- 

 pears that great beds of the Laurentian limestones are composed 

 of the ruins of the Eozobn. These rocks, which are white, crys- 

 talline, and mingled with pale-green serpentine, are similar in as- 

 pect 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 dolomitic. The accompanying strata 

 often present finely crystallized pyroxene, hornblende, phlogopite, 

 apatite, and other minerals. These observations bring the forma- 

 tion of siliceous minerals face to face with life, and show that their 

 generation was not incompatible with the contemporaneous exist- 

 ence and the preservation of organic forms. They confirm, more- 

 over, the view which I some years since put forward, that these 

 silicated minerals have been formed, not by subsequent metamojr 

 phism in deeply buried sediments, but by reactions going on at the 

 earth's surface.f In support of this view, I have elsewhere re- 

 ferred to the deposition of silicates of lime, magnesia, and iron from 

 natural waters, to the great beds of sepiolite in the unaltered Ter- 

 tiary strata of Europe; to the contemporaneous formation of neolite 

 (an alumino-magnesiau silicate related to loganite and chlorite in 

 composition) ; and to glauconite, which occurs .not only in Second- 

 ary, Tertiary, and Recent deposits, but also, as I have shown, in 

 Lower Silurian strata. J This hydrous silicate of protoxide of iron 

 and potash, which sometimes includes a considerable proportion of 

 alumina in its composition, has been observed by Ehrenberg, Man- 

 tell, and Bailey associated with organic forms in a manner which 

 seems identical with that in which pyroxene, serpentine, and lo- 

 ganite occur with the Eozoon in the Laurentian limestones. Ac- 

 cording to the first of these observers, the grains of green-sxind, or 

 glauconite, from the Tertiary limestone of Alabama are casts of 



* Recent examinations have shown that some of these masses encrusted 

 with Eozoon replaced by serpentine, consist of crystalline pyrallolite 

 (rensselaerite), which seems, like the other silicates, to have replaced 

 the organic matter of the Rhizopod. Further examinations aided by the 

 microscope, are however needed to determine with certainty the relations 

 of the Eozoon to these masses of pyrallolite. 



f Silliman's Journal [2] xxix, 284 ; xxxii, 286. Geology of Canada 

 p. 577. 



X Silliman's Journal [2] xxxiii, 277. Geology of Canada, p. 487. 



