DAWSON — LAURENTIAN GRAPHITE. 117
marine formations of more modern date ; thirdly, that if the Laurentian
graphite has been derived from vegetable matter, it has only
undergone a metamorphosis similar in kind to that which organic
matter in metamorphosed sediment of later age has experienced;
fourthly, that the association of the graphitic matter with organic
limestone, beds of iron ore, and metallic sulphides greatly strengthens
the probability of its vegetable origin; fifthly, that when we consider
the immense thickness and extent of the Eozoonal and graphitic
limestones and iron-ore deposits of the Laurentian, if we admit the
organic origin of the limestone and graphite, we must be prepared
to believe that the life of that early period, though it may have
existed under low forms, was most copiously developed, and that it
equalled, perhaps surpassed, in its results, in the way of geological
accumulation, that of any subsequent period.
In conclusion, this subject opens up several interesting fields of chemical, physiological, and geological inquiry. One of these relates to the conclusions stated by Dr. Hunt as to the probable existence of a large amount of carbonic acid in the Laurentian atmosphere, and of much carbonate of lime in the seas of that period, and the possible relation of this to the abundance of certain low forms of plants and animals. Another is the comparison already instituted by Professor Huxley and Dr. Carpenter, between the conditions of the Laurentian and those of the deeper parts of the modern ocean. Another is the possible occurrence of other forms of animal life than Eozoon and Annelids, which I have stated in my paper of 1864, after extensive microscopic study of the Laurentian limestones, to be indicated by the occurrence of calcareous fragments, differing in structure from Eozoon, but at present of unknown nature. Another is the effort to bridge over, by further discoveries similar to that of the Eozoon bavaricum of Gumbel, the gap now existing between the life of the Lower-Laurentian and that of the Primordial Silurian or Cambrian period. It is scarcely too much to say that these inquiries open up a new world of thought and investigation, and hold out the hope of bringing us into the presence of the actual origin of organic life on our planet, though this may perhaps be found to have been Prelaurentian. I would here take the opportunity of stating that, in proposing the name Eozoon for the first fossil of the Laurentian, and in suggesting for the period the name "Eozoic," I have by no means desired to exclude the possibility of forms of life which may have been precursors of what is now to us the dawn of organic existence. Should remains of still older organisms be found in those rocks now known to us only by pebbles in the Laurentian, these names will at least serve to mark an important stage in geological investigation.
