1865.] DAWSON — STRUCTURE OF EOZOON. 107 



serpentine presents many curious varieties of structure, especially 

 when associated with apatite, pyroxene, and other minerals, and 

 that it affords magnificent objects under polarized light, when 

 reduced to sufficiently thin slices. 



In connexion with these remarkable remains, it appeared desir- 

 able t > ascertain, if possible, what share these or other organic 

 structures may have had in the accumulation of the limestones 

 of the Laurentian series. Specimens were therefore selected by 

 Sir W. E. Logan, and slices were prepared under his direction. 

 On microscopic examination, a number of these were found to 

 exhibit merely a granular aggregation of crystals, occasionally with 

 particles of graphite and other foreign minerals ; or a laminated 

 mixture of calcareous and other matters, in the manner of some 

 more modern sedimentary limestones. Others, however, were 

 evidently made up almost entirely 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. Perforations, 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 other 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 character, 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 serpentine. 



