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The Laurentian Hills form, then, a granite range, stretching from Eastern Canada to the Upper Mississippi, and immediately along its base are gathered the Azoic deposits, the first stratified beds, in which the absence of life need not surprise us, since they were formed beneath a heated ocean.
The presence of phosphatic nodules and bituminous matter in some of the lowest azoic rocks, probably indicates the former existence of life at these periods. But the difficulty of understanding the absence of vast piles of fossiliferous strata, which on my theory no doubt were somewhere accumulated before the Silurian epoch, is very great.
The fact that upon the American continent, east of the Rocky Mountains, the geological formations crop out in their regular succession, from the oldest azoic and primordial deposits to the cretaceous formation, without the slightest indication of a great subsequent subsidence, seems to me the most complete and direct demonstration of my proposition.
Thus such of the first-formed strata as survived the repeated changes of level, would be practically "azoic;" like the Cambrian of our geologists. When by the washing away of the soft deposits, the hard sub-strata had been exposed in the shape of rocky islets, and a footing had thus been furnished, the pioneers of a new life might be expected to make their appearance. What would they be?
It will be my object to show, not only that the absence of the climatic and atmospheric conditions essential to organic life, as we understand it, must have rendered the previous existence of any living beings impossible, but also that the completeness of the Animal Kingdom in those deposits where we first find organic remains, its intelligible and coherent connections with the successive creations of all geological times and with the animals now living, afford the strongest internal evidence that we have indeed found in the lower Silurian formations, immediately following the Azoic, the beginning of life upon earth.
There is a great break here a leap from Archaean times on the east side to Mesozoic times on the west. The east side is millions of years the older. Here is the original Plutonic or Azoic rock which apparently has never been under the sea since it was first thrust up out of the fiery depths. The west shore, including the Palisades, belongs to a much later geologic era.
To pick fairly a good sample of a large class is not easy. The problem belongs to the science of statistics, and it is a most difficult affair for anyone whose mathematics is primitive, and mine remain azoic in spite of the half dozen manuals which I once devoutly imagined that I understood.
I have spoken of the first of these periods, the Azoic, as having been absolutely devoid of life, and I believe this statement to be strictly true; but I ought to add that there is a difference of opinion among geologists upon this point, many believing that the first surface of our globe may have been inhabited by living beings, but that all traces of their existence have been obliterated by the eruptions of melted materials, which not only altered the character of those earliest stratified rocks, but destroyed all the organic remains contained in them.
This accounts for the very scanty traces to be found in America of the secondary deposits; for the Permian, Triassic, and Jurassic beds, instead of being raised to form successive shores, along which their deposits could be accumulated in regular sequence, as had been the case with the Azoic, Silurian, and Devonian deposits in the northern part of the United States, were constantly sinking, so that the Triassic settled above the Permian, the Jurassic above the Triassic, and so on, each set of strata thus covering over and concealing the preceding one.
In the Silurian epoch following the Azoic we have the first beach on which any life stirred; it extended along the base of the Azoic beds, widening by its extensive deposits the narrow strip of land already upheaved. I propose in my next article to invite my readers to a stroll with me along that beach. Ancient history is forever indispensable to the speculative historian.
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