56 PEOCEEDINGS OF THE GEOLOGICAL SOCIETY. [NoV. 23, 



limestones. Others, however, were evidently made up almost en- 

 tirely of fragments of Eozoon, or of mixtures of these with other 

 calcareous and carbonaceous fragments which afford more or less 

 evidence of organic origin. The contents of these organic limestones 

 may be considered under the following heads : — (1) Remains of 

 Eozoon ; (2) Other calcareous bodies probably organic ; (3) Objects 

 imbedded in the serpentine ; (4) Carbonaceous matters ; (5) Per- 

 forations or worm -burrows. 



1. The more perfect specimens of Eozoon do not constitute the 

 mass of any of the larger specimens in the collection of the Survey ; 

 but considerable portions of some of them are made up of material 

 of similar minute structure, destitute of lamination and irregularly 

 arranged. Some of this material gives the impression that there 

 may have been organisms similar to Eozoon, but growing in an 

 irregular or " acervuline " manner without lamination. Of this, 

 however, I cannot be certain, and on the o.ther hand there is distinct 

 evidence of the aggregation of fragments of Eozoon in some of these 

 specimens. In some they constitute the greater part of the mass. 

 In others they are imbedded in calcareous matter of a different cha- 

 racter, or in serpentine or granular pyroxene. In most of the 

 specimens the cells of the fossils are more or less filled with these 

 minerals, and in some instances it would appear that the calcareous 

 matter of fragments of Eozoon has been in part replaced by ser- 

 pentine, 



2. Intermixed with the fragments of Eozoon above referred to, 

 are other calcareous matters apparently fragmentary. Thej^ are of 

 various angular and rounded forms, and present several kinds of 

 structure. The most frequent of these is a strong lamination, vary- 

 ing in direction according to the position of the fragments, but cor- 

 responding, as far as can be ascertained, with the diagonal of the 

 rhombohedral cleavage. This structure, though crystalline, is highly 

 characteristic of Crinoidal remains when preserved in altered lime- 

 stones. The more dense parts of Eozoon, destitute of tubuli, also 

 sometimes show this structure, though less distinctly. 



Other fragments are compact and structureless, or show only a 

 fine granular appearance ; and these sometimes include grains, 

 patches, or fibres of graphite. In Silurian limestones, fragments of 

 corals- and shells which have been partially infiltrated with bitumi- 

 nou.s matter show a structure like this. On comparison with 

 altered organic limestones of the Silurian system, these appearances 

 would indicate that, in addition to the debris of Eozoon, other cal- 

 careous structures, more like those of Crinoids, Corals, and Shells, 

 have contributed to the formation of the Laurentian limestones. 



3. In the serpentine filling the chambers of a large portion of 

 Eozoon from Burgess, C. W., there are numerous small pieces of 

 foreign matter, and the serpentine itself is laminated, indicating its 

 sedimentary nature. Some of the included fragments appear to be 

 carbonaceous, others calcareous ; but no distinct organic structure 

 can be detected in them. There are, hoAvever, in the serpentine 

 many minute rounded grains of a bright-green siliceous colour, re- 



