CHAPTER IX. 



THE EOZOON QUESTION. 



In his work on the geology of Canada, 1863, Logan described some- 

 what briefly certain forms strongly resembling fossils which were dis- 

 covered some three years earlier in the Laurentian rocks belonging to 

 the Grand Calumet series of Canada. 



The specimens represented parallel or concentric layers of crystal- 

 line pyroxene, the interstices of which were filled with crystalline 

 carbonate of lime, resembling somewhat the structure of the fossil 

 Stromatopora rugosa found in the Bird's-eye and Black River lime- 

 stone. (See fig. 124.) Logan realized the 

 fact that organic remains found entombed 

 in these limestones would, if they retained 

 their calcareous nature, be almost certainly 

 obliterated by crystallization, and it would 

 only be through the replacement of the origi- 

 nal lime carbonate by some different mineral 

 substance that there would be an} r chance of 

 the forms being preserved. Nevertheless, 

 their resemblance to fossil remains was so 

 great that, had the specimens been obtained 

 from the altered rocks of the Lower Silu- 

 rian series instead of the Laurentian, he 

 thought there would have been little hesi- 

 tancy in pronouncing them to be true fossils. 



In the Quarterly Journal of the Geolog- 

 ical Society of London for 1865 Logan 

 returned to the subject, bringing much new 

 evidence to bear. He described the oldest 

 rocks in North America as those composing 



the Laurentide Mountains of Canada and the Adirondacks of New 

 York, dividing them into the Lower and Upper Laurentian series, the 

 united thickness of which was estimated to probably exceed 30,000 

 feet, and this overlaid by a third group (the Huronian), which had 

 been estimated to be some ' 18,000 feet in thickness. In both the 

 Upper and Lower Laurentian series he found zones of limestone 

 which had sufficient volume to constitute an independent formation. 



While studying these rocks he had naturally fallen to speculating 

 upon the possible occurrence of life during the period in which they 



635 





Fig. 124. — Supposed fossil from Lau- 

 rentian limestone, a, Weathered 

 surface; b, vertical transverse sec- 

 tion (reduced about one-half). 



