1866.] GUMBEL — ON LAURENTIAN ROCKS. 91 



defined,) chains of serpentine grains, of nearly equal size, connected 

 with each other. When by means of acids the lime is removed 

 from these aggregates, a perfectly coherent serpentine skeleton is 

 in all cases obtained, which may be compared to a piece of wood 

 perforated by ants. * * * * * 



The surface of the serpentine grains is rounded, pitted, and 

 irregular ; plane surfaces and straight lines are rarely to be seen. 

 Even when dilute nitric or acetic acid has been used to remove 

 the lime, a white down-like coating is frequently found on the 

 serpentine, which does not answer to the nummuline wall of the 

 calcareous skeleton. In many cases, where the lime is very 

 crystalline, and the more- delicate organic structure obliterated, 

 small tufts of radiated crystals, apparently hornblende or tremolite, 

 are seen resting upon the serpentine. These crystals, when seen 

 in thin sections, by transmitted light, may easily give rise to 

 errors ; their formation seems to have been possible only where the 

 calcareous skeleton had been destroyed, and crystalline carbonate 

 of lime deposited in its stead ; during which time free space was 

 given for the formation of these crystalline groups. In very 

 many cases there are seen, by a moderate magnifying power, (in 

 the residue from acids) deposits of small detached cylindrical 

 stems, with some larger ones, consisting of a white matter insoluble 

 in acids. These appear to be the casts of the tubuli which 

 penetrated the calcareous skeleton, and of the less frequent stolons, 

 as will be described. 



The serpentine in these sections never appears quite homo- 

 geneous, but exhibits, on the contrary, irregular groups of small 

 dark-colored globules disseminated through the mass, without 

 however any definite indications of organic form. Still more 

 frequently, the serpentine is penetrated by irregularly reticulated 

 dark colored veins, giving to the mass a cellular aspect. 



In certain parts of the serpentine^ however, parallel lines, groups 

 of curved tube-like forms, and oval openings, clearly indicate an 

 organic structure like that of the Canadian Eozoon. The finely 

 tubulated nummuline wall of the chambers, which was discovered 

 by Carpenter, and the casts of whose tubuli appear in the 

 decalcified specimens from Canada as a soft white velvet-like 

 covering, could only be found in a few isolated cases in the 

 Bavarian specimens, but was clearly made out in a few fragments. 

 (PI. I., 4.) The somewhat oblique section shows the openings 

 of the minute tubuli. 



