INTRODUCTION. XV 



Dawson : it is labelled " Eozoon special variety mineralized 

 with loganite;" but no locality is mentioned. Hunt's speci- 

 mens were from Burgess, Canada. Their layers are of two kinds : 

 one, " a somewhat ferriferous dolomite/' yielded on analysis 

 "carbonate of magnesia 4O7, carbonate of lime, with a little per- 

 oxide of iron, 59'0=99'7;" and the other, a dark green mineral 

 silicate, called loganite, yielded " silica 35*14, alumina 10' 15, 

 magnesia 31'47, protoxide of iron 8'60, water 14*64= lOO'OO." 

 It is consequently a hydrous alumino-magnesian silicate related 

 to chlorite, and a true serpentinous mineral (pp. 4, 5). The 

 original loganite occurs in prismatic crystals, which, from their 

 measurements, Dana does not hesitate to declare to be pseudo- 

 morphs after hornblende. Serpentine is another mineral equally 

 pseudomorphic after hornblende. Therefore the fact that both 

 serpentine and loganite (which are alike pseudomorphic after 

 the same mineral) form " chamber-casts of Eozoon" affords no 

 support to the presumed organic origin of these features. Besides 

 serpentine and loganite, the mineral silicate referred to by Logan 

 and Hunt under the name of ' { white pyroxene " also " occurs 

 in immediate contact with a layer " of the former*. " White 

 pyroxene," we have reason to consider, is another pseudomorph 

 after either hornblende or augite ; so that, to some extent, it 

 also invalidates the organic hypothesis. 



The specimen we have received from Mr. Damon does not 

 quite agree with S terry Hunt's. It is made up of two kinds of 

 layers, not well defined, however, as such. The loganite, which 

 forms one of the kinds, is in dark-green crystalloids, variously 

 clustered together, and very seldom showing any traces of 

 proper cleavage; as their "fracture is granular." The other 

 layers have an opaque white colour ; but, instead of consisting of 

 calcite or dolomite (miemitef), they are composed of what 

 appears to be " white pyroxene :" imbedded in these layers are 

 siliceous crystalloids of a pale-green colour, in which respect 



* Quart. Journ. Geol. Soc. vol. xxi. p. 67. 



t We find it advantageous to restrict the term dolomite to rocks, and apply 

 that of miemite (one of the names in use) to their mineral representative. 



