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which they are traversed. The vast bulk of their strata being gneisses and mica-schists, are little fitted for architecture; but their limestones, marbles, and serpentines are often of great beauty and much sought after for ornamental purposes; while their fine-grained cleavable clay-slates afford abundant material for roofing and other multifarious appliances. Indeed it is chiefly in these old metamorphic Tocks that serpentines, variegated marbles, and roofing - slates occur—the mineral transformations to which they have been subjected giving to the former those varied shades, of colouring and figure, and to the latter that fissility or cleavage, for which they are prized. But if the rocks of these systems are of comparatively little value, their metalliferous veins are rich and numerous—gold, silver, tin, copper, antimony, manganese, iron, and other metals being abundant in most primary districts, either in the veins themselves or in the debris that has been worn and washed from them during the course of ages. These primary rocks constitute, indeed, the bulk of all our older hill-ranges, and it is only in them that the slow processes of chemical deposition have yet elaborated on a grand scale the metallic ores, and the veinstuffs with which these ores are usually associated. It is true that veins and ores occur in some of the younger formations, but not in the same variety, nor with the same richness and persistence, as those that belong to the primary and more highly metamorphic strata. Hence, it may be remarked, the importance of geological investigation in colonial and newly-discovered countries; the determination of their formations being tantamount to a declaration of their mineral and metallic wealth, or, in other words, their natural fitness for mechanical and commercial development.
Such are the great primary periods of world-history— the Laurentian, the Cambrian, and Silurian. Geologists may name and arrange them as they may, but the great fact stands unquestioned, that according to our present knowledge they form the deepest or earliest of the fossiliferous systems. Other fossiliferous strata still deeper and older may be discovered as geology extends her survey of the world's crust, but in the mean time such formations are unknown. Whole systems of strata, deeper and older than the Laurentian, may have been obliterated by metamorphic changes, but such reasoning is altogether futile. In earthhistory as in human history we must make our chronological arrangements according to our knowledge, and the furthest verge to which we have pushed our investigations must necessarily stand as the practical, though provisional, commencement. And, after all, there is something so like a beginning in these old Laurentian rocks, with their lowly eozoa, that we feel, if not at the confines, at least nearing the confines, of the possible in geological history. Observe, it matters nothing to this history though the earth had swung for untold cycles as an incandescent but gradually cooling mass. We have no means of inductively determining such a condition, and we are bound in reason to commence our history with the earliest operations we can discover in the crust. The earliest of these operations is the laying down of sediments as nature is now laying down sediments; and when we find these imbedding forms among the very lowest of organised existence and nothing higher, and find that in after-ages the higher gradually make their appearance in orderly succession, it would be abandoning all logical guidance if we did not arrive at the conviction that we were approaching, in these Laurentian quartz-rocks, schists, and serpentines, the commencement of the existing ordainings of our planet. It is true that Dr Dawson's discovery of worm-burrows in the upper Laurentians, if further corroborated, would carry the inference
of Life-beginnings still lower than the lowermost Lanrentians, and into strata which, in the absence of fossil remains, we are in the habit of designating " metamorphic;" but then be it observed that the distance in time between the upper and lower Laurentians is very vast, and that the carrying of lowly life-forms even beyond the Laurentian epoch does not materially affect the conclusion. It is merely believed we are approaching, not asserted we have reached, the ultimate limit of vitality.
Of course everything connected with these investigations is as yet dim and difficult. We know next to nothing of the areas occupied by Laurentian and Cambrian strata, and can only sketch in very general terms the boundaries of the Silurian. We know nothing of the lands from which the Laurentian and Cambrian sediments were borne, and can only dimly indicate the direction from which some of the Silurian were transported. The vast thickness of these formations, the frequent alternations of their strata, and the fineness of the sediments, imply long lapses of time— but how long it were in vain, without some standard of comparison, to inquire; and even though we could give the time numerical expression in years and centuries, we could form no adequate conception of its immensity. All that we know for certain is, that the earth in these primeval periods had its seas and continents—seas in which sediments were deposited, and lands from which the material must have been borne. With the exception of a few Silurian stems and seed-vessels, we are in utter ignorance of the life and aspects of these lands; and are merely left to infer the existence of other forms of life from the presence of those we have determined. Of the tenantry of the seas we know that they were few and simple at first; but, as time rolled on, newer and higher types made their appearance, and this not only in greater numerical abundance, but in greater specific variety. No doubt the record is very imperfect, and we cannot for a moment suppose that all the forms of life have been revealed by the few scattered patches geologists have examined. Still, there must be a meaning in these lowliest forms of life coming first, in their comparative scantiness in the earliest formations, in the gradual appearance of higher and higher forms, and in their increasing abundance and specific variety; and that meaning, if we would interpret without bias or predilection, is surely this—that in these old formations we are approaching—if indeed we have not already reached—the dawning of life and the first orderings of that system of progression that still prevails, and is carrying the present along with it.
Such, once more, is the faint and fragmentary history of the earth's primal periods—dim and shadowy loomings of undiscovered lands; glimpse of broad seas in which the lowlier forms of life spread and increased in numbers, and rose by some great creative law through newer species to higher and higher orders. Fragmentary as the history may seem, it is truly marvellous that science, dealing with such obscure materials, should have been able, within little more than a quarter of a century, to arrive at such satisfactory conclusions. Within the memory of living geologists these Silurian, Cambrian, and Laurentian systems were the "Transition," "Metamorphic," "Hypozoic" (under life), and "Azoic" (void of life) rocks of the systematists; and now each and all of them have yielded their life-forms— proving the great fact, that there is no known period of the earth's history when life, in some form or other, did not exist, and leading to the belief that the manifestation of life on our planet was coeval with the earliest of the stratified formations. How wonderful the interest with which these chips and fragments can invest the history of the past! Like the prehistoric relics of the shell-mounds, the lake-dwellings, the caves, and the river-gravels, they may lead to no very definite or connected view of the aspects and history of the periods to which they relate; but to science they are invaluable as proving what has been there, and as indicating the design and method of creation. Where everything is so obscure the faintest glimmer becomes an unspeakable boon—a certainty of itself wherefrom to predicate, and the strongest incentive to further investigation.