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The Keweenawan is composed of immense piles of lava, such as those of Iceland, overlain by bedded sandstones. What remains of these rock systems after the denudation of all later geologic ages is enormous. The Lower Huronian is more than a mile thick, the Upper Huronian more than two miles thick, while the Keweenawan exceeds nine miles in thickness.
The mineral character of the Upper Laurentian differs, as we have seen, from that of the Lower, and the pebbles of gneiss in the Huronian conglomerates are thought to prove that the Laurentian strata were already in a metamorphic state before they were broken up to supply materials for the Huronian.
The talk washed back and forth across the hulks of classic sea mysteries, new and old; of the City of Boston, which went down with all hands, leaving for record only a melancholy scrawl on a bit of board to meet the wondering eyes of a fisherman on the far Cornish coast; of the Great Queensland, which set out with five hundred and sixty-nine souls aboard, bound by a route unknown to a tragic end; of the Naronic, with her silent and empty lifeboats alone left, drifting about the open sea, to hint at the story of her fate; of the Huronian, which, ten years later, on the same day and date, and hailing from the same port as the Naronic, went out into the void, leaving no trace; of Newfoundland captains who sailed, roaring with drink, under the arches of cathedral bergs, only to be prisoned, buried, and embalmed in the one icy embrace; of craft assailed by the terrible one-stroke lightning clouds of the Indian Ocean, found days after, stone blind, with their crews madly hauling at useless sheets, while the officers clawed the compass and shrieked; of burnings and piracies; of pest ships and slave ships, and ships mad for want of water; of whelming earthquake waves, and mysterious suctions, drawing irresistibly against wind and steam power upon unknown currents; of stout hulks deserted in panic although sound and seaworthy; and of others so swiftly dragged down that there was no time for any to save himself; and of a hundred other strange, stirring and pitiful ventures such as make up the inevitable peril and incorrigible romance of the ocean.
Cambrian Rocks of the United States and Canada. Potsdam Sandstone. Huronian Series. Laurentian Group, upper and lower. Eozoon Canadense, oldest known Fossil. Fundamental Gneiss of Scotland.
They are not only more ancient than the fossiliferous Cambrian formations above described, but are older than the Huronian last mentioned, and had undergone great disturbing movements before the Potsdam sandstone and the other "primordial" or Cambrian rocks were formed. The older half of this Laurentian series is unconformable to the newer portion of the same.
These dolerites are cut through by intrusive syenite, and this syenite, in its turn, is again cut and penetrated by feldspar porphyry, the base of which consists of petrosilex, or a mixture of orthoclase and quartz. All these trap- rocks appear to be of Laurentian date, as the Cambrian and Huronian rocks rest unconformably upon them. General Aspect of Plutonic Rocks. Granite and its Varieties.
In February, 1892, the Naronic, from Liverpool for New York; in the same month in 1896, the State of Georgia, from Aberdeen for Boston; in February, 1899, the Alleghany, from New York for Dover; and once more in February, 1902, the Huronian, from Liverpool for St. John's all disappeared without leaving a trace.
Next below the Upper Cambrian occur strata called the Huronian by Sir W. Logan, which are of vast thickness, consisting chiefly of quartzite, with great masses of greenish chloritic slate, which sometimes include pebbles of crystalline rocks derived from the Laurentian formation, next to be described.
Great unconformities, UU' separate the Algonkian both from the Archean and from the Cambrian, and divide it into three distinct systems, the LOWER HURONIAN, the UPPER HURONIAN, and the KEWEENAWAN. The Lower and the Upper Huronian consist in the main of old sea muds and sands and limy oozes now changed to gneisses, schists, marbles, quartzites, slates, and other metamorphic rocks.
Parts of the original skeleton, consisting of carbonate of lime, are still preserved; while certain inter-spaces in the calcareous fossil have been filled up with serpentine and white augite. On this oldest of known organic remains Dr. The Laurentian and Huronian rocks united are about 50,000 feet in thickness, and the Lower Laurentian was disturbed before the newer series was deposited.
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