will be rendered intelligible to all by the explanations in the text.

There seems to be but little poetry in the attempt to unravel the thread of chemical reactions which followed each other upon the earth in those dim and twilight ages; but it is certainly an inspiring development of late researches that the sceptre which chemistry sways over the modern world is the same which she wielded over the mute atoms of the forming crust.

It appears, from what has been suggested, that a portion of those ancient strata originated from sediments mechanically deposited, and another portion from chemical precipitates thrown down while the elements were adjusting themselves according to their strongest affinities.

The reader should not imagine that the proofs of these things are afar off. They lie within the scope of his own observation and verification. If you can not gaze upon the frowning summit of Katahdin, or the dark and lichencovered sides of the Adirondacs, nor the upturned piles of stony lumber which make the ridges of the Appalachians, nor the acres of rocky floor torn up for your inspection along the shores of the upper lakes, examine some of the specimens which Nature has brought from those northern regions to your very doors. Scattered over your fields may be found fragments of the underlying unstratified granite and sienite, diorite and dolerite. Here, too, are fragments of rocks formed of the same constituents as these, but under a stratified arrangement. The most striking of these are the gneisses, where the various colored minerals set forth the stratification with distinctness. These came from the thick beds resting upon the crystalline foundation of the earth's crust. They are the ruins— a second time ruined-of some ancient rocky shore which the fury of the elements has reduced to sand. Here are

boulders of quartz, liberated from its ancient combinaHere are tions and precipitated in the bottom of the sea. boulders of sandstone-vitreous, half-fused sandstonebetter known as "hard-heads," which consist of grains of quartz produced by the grinding up of some more ancient quartz rock. These grains have been again cemented together, and a convulsion of Nature has sent them a second time vagrants over the surface of the earth. Here, too, are fragments of those ancient marbles, precipitated at the time. when the partners of the ancient chlorides and carbonates formed new copartnerships for life. These all, rounded and battered by long travel, have come from their ancient homes in those northern regions where our continent first raised its head to scowl defiance at the supremacy of tempest and flood. They constitute, with numberless specimens of rocks of every other age, a grand museum, where every student of Nature may roam and study at his pleas

ure.

The chemical reactions, and precipitations, and sedimentary accumulations to which I have referred extended over an immense interval of time. During this long period materials accumulated at the bottom of the sea to the thick-ness of more than twenty-five thousand feet. Their geographical extent corresponded with that of the primeval sea. We find these rocks on every side of the globe, perforated here and there by the original granitic summits, which serve to point out to us the sites of the oldest islands. For our knowledge of the vast thickness of these older strata, their composition, and their wide American distribution, we are indebted to Sir William Logan and his associates of the Geological Commission of Canada. Sir William has ascertained that this stupendous pile of strata is properly divisible into two great systems, the lower of which he styles the "Laurentian," from the great

river along whose valley they have been studied, while the upper is denominated the "Huronian," from the lake upon whose northern shores the upper members of the series are so finely exposed. The iron-bearing rocks of the northern peninsula of Michigan belong to the Huronian system, as well as those of Southeastern Missouri and Northern New York.

CHAPTER VII.

A RAY OF LIFE.

DURING the progress of that primeval age which wit

nessed the war of elements that I have already sketched, there was little opportunity for the unfolding of organic existence. The atmosphere was unfit for respiration; and the waters, if not too highly heated, were nevertheless charged with impurities destructive to both vegetable and animal life. It was a dreary and monotonous age, with nothing of that which now beautifies and diversifies the face of nature. The same sunlight fell upon the heaving waters of that tenantless and gloomy sea, and the same tide-wave performed its everlasting circuit round the globe. There was little diversity of weather or climate. The continents and mountain ridges, which give birth to oceanic and atmospheric currents, had not yet appeared above the wave. But there must have been a succession of seasons. The winter's sun, as now, went early to his couch, and his tardy rising belated the December mornings. His unequal favors to the different latitudes necessitated the trade winds and the great equalizing currents of the ocean. The higher density of the primeval atmosphere rendered it more retentive of the solar heat, and thus contributed greatly to diminish the rate of terrestrial cooling by radiation into space. Evaporation proceeded at a rapid rate, and condensation and precipitation were correspondingly copious. It was probably a stormy period, like the showery season which succeeds the protracted storm of the vernal equinox.

It would seem almost inevitable that the temperature and constitution of the primeval sea should be incompatible equally with vegetable and animal life. It is true that both plants and animals are now known to flourish under conditions of heat and cold, and chemistry, which are entirely at variance with the general notions of organic adaptability. Certain plants, for instance, are reported as flourishing in the boiling geysers of Iceland and the hot springs of California. Others make their habitat upon the snows of Greenland, and impart the ruddy glow of warmth even in the undisputed empire of frost. The germs of vegetable, and even of animal life, populate every element and every locality; and only a temperature of some hundreds of degrees suffices to rid a fluid exposed to the air of all the vitalized germs that inhabit it. The egg of an insect, stuck in the crevice of the bark of an apple-tree, endures the rigors of a Canadian winter; and the organized chrysalis seems, in many cases, to possess equal powers of resisting cold. It is unsafe, then, to attempt to determine at what epoch the waters of the primeval sea became sufficiently cooled and purified to receive the first organic forms. There was, in all probability, an earliest epoch that was completely destitute of organic forms. But, to ascertain its beginning and its end, Geology must yet apply herself to a closer study of the monuments of the gneissic age.

Reasoning deductively, it is equally presumable that vegetable life preceded animal life in order of appearance. Vegetable life is capable of enduring more extreme conditions. Vegetation could better tolerate the excess of carbonic acid in the atmosphere and the waters. Vegetation, moreover, is capable of drawing its sustenance from the mineral world, while animals rely exclusively upon organic food. The vegetable stands between the animal and