Other discoveries also are foreshadowed here. The microscope may yet detect the true nature and affinities of some of the fragments associated with Eozoon. Less altered portions of the Laurentian rocks may be found, where even the vegetable matter may retain its organic forms, and where fossils may be recognised by their external outlines as well as by their internal structure. The Upper Laurentian and the Huronian have yet to yield up their stores of life. Thus the time may come when the rocks now called Primordial shall not be held to be so in any strict sense, and when swarming dynasties of Protozoa and other low forms of life may be known as inhabitants of oceans vastly ancient as compared with even the old Primordial seas. Who knows whether even the land of the Laurentian time may not have been clothed with plants, perhaps as much more strange and weird than those of the Devonian and Carboniferous, as those of the latter are when compared with modern forests?
NOTES TO CHAPTER III.
(A.) Sir William E. Logan on the Discovery and Characters of Eozoon.
[Journal of Geological Society, February, 1865.]
"In the examination of these ancient rocks, the question has often naturally occurred to me, whether during these remote periods, life had yet appeared on the earth. The apparent absence of fossils from the highly crystalline limestones did not seem to offer a proof in the negative, any more than their undiscovered presence in newer crystalline limestones where we have little doubt they have been obliterated by metamorphic action; while the carbon which, in the form of graphite, constitutes beds, or is disseminated through the calcareous or siliceous strata of the Laurentian series, seems to be an evidence of the existence of vegetation, since no one disputes the organic character of this mineral in more recent rocks. My colleague, Dr. T. Sterry Hunt, has argued for the existence of organic matters at the earth’s surface during the Laurentian period from the presence of great beds of iron ore, and from the occurrence of metallic sulphurets;[O] and finally, the evidence was strengthened by the discovery of supposed organic forms. These were first brought to me, in October, 1858, by Mr. J. McMullen, then attached as an explorer to the Geological Survey of the province, from one of the limestones of the Laurentian series occurring at the Grand Calumet, on the river Ottawa.
[O] Quarterly Journal of the Geological Society, xv., 493.
"Any organic remains which may have been entombed in these limestones would, if they retained their calcareous character, be almost certainly obliterated by crystallization; and it would only be by the replacement of the original carbonate of lime by a different mineral substance, or by an infiltration of such a substance into all the pores and spaces in and about the fossil, that its form would be preserved. The specimens from the Grand Calumet present parallel or apparently concentric layers resembling those of Stromatopora, except that they anastomose at various points. What were first considered the layers are composed of crystallized pyroxene, while the then supposed interstices consist of carbonate of lime. These specimens, one of which is figured in Geology of Canada, p. 49, called to memory others which had some years previously been obtained from Dr. James Wilson, of Perth, and were then regarded merely as minerals. They came, I believe, from masses in Burgess, but whether in place is not quite certain; and they exhibit similar forms to those of the Grand Calumet, composed of layers of a dark green magnesian silicate (loganite); while what were taken for the interstices are filled with crystalline dolomite. If the specimens from both these places were to be regarded as the result of unaided mineral arrangement, it appeared to me strange that identical forms should be derived from minerals of such different composition. I was therefore disposed to look upon them as fossils, and as such they were exhibited by me at the meeting of the American Association for the Advancement of Science, at Springfield, in August, 1859. See Canadian Naturalist, 1859, iv., 300. In 1862 they were shown to some of my geological friends in Great Britain; but no microscopic structure having been observed belonging to them, few seemed disposed to believe in their organic character, with the exception of my friend Professor Ramsay.
"One of the specimens had been sliced and submitted to microscopic observation, but unfortunately it was one of those composed of loganite and dolomite. In these, the minute structure is rarely seen. The true character of the specimens thus remained in suspense until last winter, when I accidentally observed indications of similar forms in blocks of Laurentian limestone which had been brought to our museum by Mr. James Lowe, one of our explorers, to be sawn up for marble. In this case the forms were composed of serpentine and calc-spar; and slices of them having been prepared for the microscope, the minute structure was observed in the first one submitted to inspection. At the request of Mr. Billings, the palæontologist of our Survey, the specimens were confided for examination and description to Dr. J. W. Dawson, of Montreal, our most practised observer with the microscope; and the conclusions at which he has arrived are appended to this communication. He finds that the serpentine, which was supposed to replace the organic form, really fills the interspaces of the calcareous fossil. This exhibits in some parts a well-preserved organic structure, which Dr. Dawson describes as that of a Foraminifer, growing in large sessile patches after the manner of Polytrema and Carpenteria, but of much larger dimensions, and presenting minute points which reveal a structure resembling that of other Foraminiferal forms, as, for example Calcarina and Nummulina.
"Dr. Dawson’s description is accompanied by some remarks by Dr. Sterry Hunt on the mineralogical relations of the fossil. He observes that while the calcareous septa which form the skeleton of the Foraminifer in general remain unchanged, the sarcode has been replaced by certain silicates which have not only filled up the chambers, cells, and septal orifices, but have been injected into the minute tubuli, which are thus perfectly preserved, as may be seen by removing the calcareous matter by an acid. The replacing silicates are white pyroxene, serpentine, loganite, and pyrallolite or rensselaerite. The pyroxene and serpentine are often found in contact, filling contiguous chambers in the fossil, and were evidently formed in consecutive stages of a continuous process. In the Burgess specimens, while the sarcode is replaced by loganite, the calcareous skeleton, as has already been stated, has been replaced by dolomite, and the finer parts of the structure have been almost wholly obliterated. But in the other specimens, where the skeleton still preserves its calcareous character, the resemblance between the mode of preservation of the ancient Laurentian Foraminifera, and that of the allied forms in Tertiary and recent deposits (which, as Ehrenberg, Bailey, and Pourtales have shown, are injected with glauconite), is obvious.