1864.] DAWSON— STRUCTURE OF EOZOON. 55 



hand, there are large specimens in the collection of the Canadian 

 Survey, in which the lower and older parts of the masses of Eozoon 

 are mineralized with pyroxene, and have to a great extent lost the 

 perfection of structure which characterizes the more superficial parts 

 of the same masses, in which the chambers have been filled with a 

 light-green serpentine. Dr. Steriy Hunt has directed his attention to 

 the conditions of deposit of these minerals, and wiU, I have no doubt, 

 be able satisfactorily to explain the manner in which they may have 

 been introduced into the chambers of the fossils without destroying 

 the texture of the latter. 



It is due to Dr. Sterry Hunt to state that, as far back as 1858, in a 

 paper published in the Quarterly Journal of the Geological Society*, 

 he insisted on certain chemical characters of the Laurentian beds as 

 affording " evidence of the existence of organic life at the time of 

 the deposition of these old crystalline rocks," and that he has 

 zealously aided in the present researches. 



I may also state that Mr. Billings, the palaeontologist of the 

 Survey, has joined in the request that I should undertake the ex- 

 amination and description of the specimens, as being more specially 

 a subject of microscopical investigation. 



Before concluding this part of the subject, it is proper to observe 

 that the structures above described can be made out only by the 

 careful study of numerous slices, and in some instances only with 

 polarized light. Even in the more perfect specimens of Eozoon, as 

 those accustomed to such researches will readily understand, the 

 accidents of good preservation and the cutting of the slices in the 

 proper place and direction must conspire in order to a clear defini- 

 tion of the more minute structures. 



It is also to be observed that the specimens present numerous 

 remarkable microscopic appearances, depending on crystaUization 

 and concretionary action, which must not be confounded wdth organic 

 structure. It would be out of place to give any detailed descrip- 

 tion of them here, but it is necessary to caution observers unaccus- 

 tomed to the examination of mineral substances under the microscope, 

 as to their occurrence. I may also mention that the serpentine 

 presents many curious varieties of structure, especially when asso- 

 ciated with apatite, pyroxene, and other minerals, and that it 

 affords magnificent objects under polarized light, when reduced to 

 sufiiciently thin slices. 



In connexion with these remarkable remains, it appeared desirable 

 to ascertain, if possible, what share these or other organic structures 

 may have had in the accumulation of the limestones of the Lauren- 

 tian series. Specimens were therefore selected by Sir "VV. E. Logan, 

 and slices were prepared under his direction. On microscopic exa- 

 mination, a number of these were found to exhibit merely a granidar 

 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 



* Vol. xv. p. 493. 



