1865.] HUNT — MINERALOGY OP EOZOON. 123 



15*40 ; z=r 100-92. These serpentines from the Laurentian lime- 

 stones are remarkable for their freedom from iron-oxide, for their 

 their large amount of water, and their low specific gravity.* 



Specimens of Eozoon from Burgess differ from the foregoing in 

 the composition both of the replacing material and septa. The 

 latter consist of a somewhat ferriferous dolomite, the analysis of 

 which was made upon portions mechanically separated from the 

 enclosed silicate : it yielded carbonate of magnesia 40-7, carbonate 

 of lime,with a little peroxide of iron, 59-0 ; = 99'7. The septa of the 

 specimen from this locality are in some parts more than 30 milli- 

 metres in thickness, and exhibit the chambers, cells, and septal 

 orifices ; but no tubuli are seen. The replacing material has the 

 hardness of serpentine, for which it was at first mistaken. Its 

 color is blackish-green ; but olive-green in thin sections, when it 

 is seen by transmitted light to be crystalline in texture. Its frac- 

 ture is granular, and its lustre feebly shining. It is decomposed 

 by heated sulphuric acid, and was thus analyzed, yielding the re- 

 sult I. The centesimal composition of the soluble portion is given 

 under II. 



I. II. in. 



Silica 33-75 35-14 36-50 



Alumina 9-75 10-15 10-80 



Magnesia 30-24 31-47 28-20 



Protoxide of iron 8-19 8-60 9-54 



Water 14-08 14-64 14-62 



Insoluble sand 2-50 



98-51 100-00 99-66 



The silicate which here takes the place of the pyroxene and ser- 

 pentine observed in the other specimens of Eozoon is one of fre- 

 quent occurrence in the Laurentian limestones, and appears to con- 

 stitute a distinct species, which I "long since described under the 

 name of loganite, and which occurs at the Calumet in dark brown 

 prismatic crystals, j I have since observed a similar mineral in 

 two other localities besides the one here noticed. The result III, 

 which is placed by the side of the analysis of the Burgess fossil, 

 was obtained with a greenish-grey sparry prismatic variety from 

 North Elmsley, having a hardness of 3*0, and a specific gravity of 



* See my descriptions, Silliman's Journal [2] xxvi, 236. 

 f Phil. Mag., 4th ser., vol. ii, p. 65. 



