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How far the Transfer of Sediment from the Land to a neighbouring Sea-bottom may affect Subterranean Movements. Permanence of Continental and Oceanic Areas. The reader has been already informed that, in the structure of the earth's crust, we often find proofs of the direct superposition of marine to fresh-water strata, and also evidence of the alternation of deep-sea and shallow-water formations.
In order that strata of shallow-water origin should be able to attain a thickness of several thousand feet, and so come to exert a considerable downward pressure, there must have been first some independent and antecedent causes at work which have given rise to the incipient shallow receptacle in which the sediment began to accumulate.
Between the Carboniferous and Silurian strata there intervenes, in the United States and Canada, a great series of formations referable to the Devonian group, comprising some strata of marine origin abounding in shells and corals, and others of shallow-water and littoral origin in which terrestrial plants abound.
The rocks of these series are shallow-water deposits and reach the total thickness of some five thousand feet. Evidently they were laid over an area which was on the whole gradually subsiding, although with various gentle oscillations which are recorded in the different formations.
Now, the lower part of the clay, near here, contains shallow-water shells: but if you went forty miles to the eastward, you would find in the corresponding lower beds of the clay, deep- water shells, and far above them, shallow-water shells such as you find here: a fact which shows plainly that this end of the clay sea was shallowest, and therefore first filled up.
The common or reef-building coral has but little use except as a source of lime, and no intrinsic value except as an object of curiosity. Coral reefs may be arranged under three classes; namely, fringing reefs, barrier reefs, and atolls. The first class embraces the shallow-water reefs found close to land, either surrounding islands or skirting the shores of continents.
The materials for the petrifaction of organic remains are, therefore, usually at hand in a state of chemical solution wherever organic remains are imbedded in new strata. Why the Position of Marine Strata, above the Level of the Sea, should be referred to the rising up of the Land, not to the going down of the Sea. Strata of Deep-sea and Shallow-water Origin alternate.
From the south point of Clarence Strait it is distant eleven miles, and the bay in which it lies, from the shallow-water at the head of it, was called Shoal Bay. The boat being provisioned for four days, we pushed on to explore another opening above fifteen miles to the westward.
In these cases we as frequently find fresh-water beds below a marine set or shallow-water under those of deep-sea origin as the reverse. Thus, if we bore an artesian well below London, we pass through a marine clay, and there reach, at the depth of several hundred feet, a shallow-water and fluviatile sand, beneath which comes the white chalk originally formed in a deep sea.
He lived to see the paddle-wheel grow in importance and estimation as a means of propulsion only in turn to be supplanted by the screw-propeller, which gradually increased in engineering favor from the days of its obscure infancy until it became the only means employed for the propulsion of ships navigating the high seas, while it had become a most serious rival to the paddle-wheel even for the purposes of interior and shallow-water navigation, long a field considered as peculiarly suited to the paddle-wheel and to the engines adapted to its operation.
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