1865.] HUNT — MINERALOGY OF EOZOON. 121 



chambers, cells, and canals left vacant by the disappearance of 

 the animal 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 understood that 

 when the replacement of the Eozo'on 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 process of infiltration, in which the silicates 

 were deposited from solution in water, like the silica which 

 fills up the pores of wood in the process of silicification. The 

 replacing silicates, so far as yet observed, 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 relations of the carbonate 

 and the silicates are well seen in thin sections under the micro- 

 scope, especially by polarized light. The calcite, dolomite, and 

 pyroxene exhibit their crystalline structure to the unaided eye ; 

 and the serpentine and loganite are also seen to be crystalline 

 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 Eozo'on. 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 replacing mineral is serpen- 

 tine, although very perfect specimens are sometimes found in 

 pyroxene. The crystallization of the latter mineral appears, how- 

 ever, in most cases to have disturbed the calcareous septa. 



Serpentine and pyroxene are generally associated in these 

 specimens, as if their disposition had marked different stages of a 

 continuous 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 translu- 

 cent serpentine occurs in immediate contact with the white pyrox- 

 ene. The calcareous septa in this specimen are very thin, and are 



