1864.] STERBY HUNT — EOZOON. 69 



specimen from this locality are in some parts more than 3-0 milli- 

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

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

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

 colour 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 result I. 

 The centesimal composition of the soluble portion is given under II. 



X. II. III. 



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 frequent 

 occurrence in the Laurentiau limestones, and appears to constitute 

 a distinct species, which I long since described under the name of 

 loganite, and which occurs at the Calumet in dark-brown prismatic 

 crystals*. I have since observed a similar mineral in two other loca- 

 lities 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 2-539 f. These hydrous 

 alumino-magnesian silicates, which I have there included under the 

 name of loganite, are related to chlorite and to pyrosclerite in com- 

 position, but are distinguished by their eminently foliated micaceous 

 structure. 



When examined under the microscope, the loganite, which replaces 

 the Eozoon of Burgess, shows traces of cleavage-lines, which indi- 

 cate a crystalline structure. The grains of insoluble matter found 

 in the analysis, chiefly of quartz-sand, are distinctly seen as foreign 

 bodies imbedded in the mass, which is moreover marked by lines 

 apparently due to cracks formed by a shrinking of the silicate, and 

 subsequently filled bj a further infiltration of the same material. 

 This arrangement resembles on a minute scale that of septaria. 

 Similar appearances are also observed in the serpentine which re- 

 places the Eozoon of Grenville, and also in a massive serpentine from 

 Burgess resembling this, and enclosing fragments of the fossil. In 

 both of these specimens also grains of mechanical impurities are 

 detected by the microscope, which are, however, rarer than in the 

 loganite of Burgess. 



From the above facts it may be concluded that the various sili- 



* Phil. Mag. 4th ser. vol. ii. p. 65. 

 . t For a description of this and similar silicates, see ' Geology of Canada,' p. 491 . 



