70 J. W. DAWSON ON THE OCCURRENCE OF 



long parallel tubes, and with little development of supplemental 

 or intermediate skeleton. The appearance of parallel tubulation 

 running through and past several successive chamberlets was more 

 conspicuous in these specimens than in the ordinary acervuline 

 Eozoon, and the chamberlets themselves more cylindrical and tortu- 

 ous. These specimens may either be portions of the acervuline 

 superficial part of Eozoon broken off and separately preserved, or 

 they may constitute a distinct varietal form. As the latter seems on 

 the whole most probable, I would name this form variety acervxdina. 



These varieties are of much more rare occurrence than the ordi- 

 nary type of Eozoon. 



The ordinary specimens of Eozoon found at St. Pierre are mineral- 

 ized with serpentine ; but fragments imbedded in the dolomitic 

 limestones have their canals filled with a transparent mineral which, 

 from its optical character, is evidently dolomite, though the quan- 

 tity obtained was not sufficient for any definite chemical test. 

 Parts of the canals in these specimens were filled with calcite, as 

 shown by its dissolving entirely away in a dilute acid. In one of 

 the serpentiuous specimens also I have observed that, while portions 

 of the groups of canals, especially the basal portions, are filled with 

 serpentine, the extremities of the canals and their finer branches 

 present, under polarized light, the aspect of calcite ; and that they 

 are filled with this mineral is proved by tbese portions of the canal- 

 filling being entirely removed when treated with dilute acid. It 

 would thus appear that in these specimens, while the terminal parts 

 of the canals have been filled with calcite, the basal portions have 

 been occupied by serpentine. This is not, however, a new fact, as 

 similar appearances have been already described both by Dr. Car- 

 penter and the writer. 



In one specimen I observed a portion of the fossil entirely replaced 

 by serpentine, the walls of the skeleton being represented by a 

 lighter-coloured serpentine than that filling the chambers, and still 

 retaining traces of the canals. The walls thus replaced by serpen- 

 tine could be clearly traced into connexion with the portions of 

 those still existing as calcite. This shows that the serpentine, like 

 the quartz in silicificd shells and corals, has had the power of re- 

 placing the calcite of the fossils ; and I believe that its partial 

 action in this way accounts for some irregularities observed in the 

 less perfectly preserved specimens. Nor is it improbable, as Dr. 

 Hunt has already suggested, that some of the masses of serpentine 

 and pyroxene on which specimens of Eozoon are based, may represent 

 older and more perfectly mineralized masses of the fossil. 



In some of the specimens of Eozoon, the superficial laminae are 

 apparently broken and displaced in such a manner as to suggest 

 the idea that partial disintegration by the waves had taken place 

 before they were finally buried. It is also observable that in some 

 of the masses the compression to which they have been subjected 

 has produced a microscopic faulting, which slightly displaces the 

 laminae. 



One of the most interesting features of the St.-Pierre limestone, 



