1864.] STEKRY HUNT EOZOON. 67 



4. On the Mineeaiogt of ceetain Oeganic Eemains from the Latt- 

 KENTiAN EocKS of Canada. By T. Sterry Hunt, Esq., M.A., F.E.S. 



[Communicated by Sir W. E. Logan, LL.D., RE.S., F.G.S.] 



The remains of Eozoon Canadense, a Foraminiferal organism re-^ 

 cently discovered in the Laurentian limestones of Canada, present 

 an interesting subject of study, both to the mineralogist and the 

 geologist. For a zoological description of this organic form the 

 reader is referred to the preceding description by Dr. Dawson. 



The details of structure have been preserved by the introduction 

 of certain mineral silicates, which have not only filled up the cham- 

 bers, cells, ard canals left vacant by the disappearance of the ani- 

 mal matter, but have in very many cases been injected into the 

 tubuli, filling even their smallest ramifications. These silicates have 

 thus taken the place of the original sarcode, while the calcareous septa 

 remain. It will then be xinderstood that when the replacement of 

 the Eozoon by silicates is spoken of, this is to be understood of the 

 soft parts only, since the calcareous skeleton is preserved, in most 

 cases, without any alteration. The vacant spaces left by the 

 decay of the sarcode may be supposed to have been filled by a pro- 

 cess of infiltration, in which the sUicates were deposited from solu- 

 tion in water, like the silica which, fills up the pores of wood in the 

 process of silicification. The replacing silicates, so far as yet ob- 

 served, are a white pyroxene, a pale-green serpentine, and a dark- 

 green alumino-magnesian mineral, which is allied in composition to 

 chlorite and to pyrosclerite, and which I have referred to loganite. 

 The calcareous septa in the last case are found to be dolomitic, but 

 in the other instances are nearly pure carbonate of lime. The rela- 

 tions of the carbonate and the silicates are well seen in thin sections 

 under the microscope, especially by polarized light. The calcite, 

 dolomite, and pyroxene exhibit their crystalline structure to the 

 unaided eye ; and the serpei?tine and loganite are also seen to be 

 cr_ystalline when examined with the microscope. "When portions of 

 the fossil are submitted to the action of an acid, the carbonate of 

 lime is dissolved, and a coherent mass of serpentine is obtained, 

 which is a perfect cast of the soft parts of the Eozoon. The form of 

 the sarcode which filled the chambers and cells is beautifully shown, 

 as well as the connecting canals and the groups of tubuli ; these latter 

 are seen in great perfection upon surfaces from which the carbonate 

 of lime has been partially dissolved. Their preservation is generally 

 most complete when the replac'ug mineral is serpentine, although very 

 perfect specimens are sometimes found in pyroxene. The crystal- 

 lization of the latter mineral appears, however, in most cases to have 

 disturbed the calcareous septa. 



Serpentine and pyroxene are generally associated in these speci- 

 mens, as if their deposition had marked different stages of a con- 

 tinuous process. At the Calumet, one specimen of the fossil exhibits 

 the whole of the sarcode replaced by serpentine ; while, in another 

 one from the same locality, a layer of pale-green translucent serpen- 

 tine occurs in immediate contact with the white pyroxene. 



e2 



