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CHAPTER VI.

OLD OCEAN COMMENCES WORK.

THOUSAND years of storm and lightning have passed, and the primeval tempest is drawing to a close. The waters are now permitted to rest upon the surface. By degrees the clouds are exhausted, and sunlight filters through the thinned envelope. As the morning of another geological epoch dawns, it reveals the change of scene. The surface which, in the preceding age, was scorched and arid, is now a universal sea of tepid waters. The earliest ocean enveloped the earth on every hand. A few isolated granite summits perhaps protruded above the watery waste. Around their bases careered the surges which gnawed at their foundations. Geology is unable to aver that any of them survived the denudations of this first detrital period. The demands of nature for material from which to lay the thick and massive foundations of the stratified pile of rocks were enormous, and it is probable that whole mountains were quarried level by the energies of this young, fresh, and all-embracing ocean. Probably, however, the nuclei of some of our oldest mountain masses, though subsequently elevated to their present altitudes, may be regarded as the remnants of the granite knobs that reared their frowning and angular visages above the primordial deep. If so, the erosion of the waves and the battering of the tempests have given to their sides and heads a smooth and bald rotundity. But most, if not all of the original pinnacles of the earth's crust have been leveled to the water's surface and spread over the floor of the

sea. To-day we may gather up the fragments, not from the bottom of the sea, but raised again mountain high, or incorporated into the fabric of new-built continents! Sublime ruins! What are the marbles of Nineveh, or the columns of the Parthenon, in comparison with these hoary relics of Nature's primeval structures?

I said that the fury of the waves strewed the ocean's bed with the ruins of these ancient islands. This is no fancy. The demonstration is before our eyes. The floor of the sea was first formed of rocks that had cooled from a state of fusion. The few islands that existed were but exposed portions of this floor. The débris scattered over this foundation would be arranged in layers, as water always arranges its sediments. The coarser materials would be transported by the more powerful action and deposited in one place; the finer materials would be carried beyond by

Fig. 15. Shore Erosion and Distribution of Sediments.

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a, a. The primordial igneous crust. b. A sea-side cliff gnawed by the waves. The ordinary sea-level. d. The ruins of the cliff-the coarser deposited near the shore, and the finer floated to greater depths.

the feebler agency, and deposited in a remoter region. Thus some of the first-formed strata would be finer and others would be coarser; but all must be composed of materials derived from the pre-existing rocks. This deduction is again corroborated by well-known facts. Every where do we find reposing upon the ancient igneous floor a bed of stratified materials composed of the same constituent

minerals as the rocks they rest upon. For instance, granite is very commonly the foundation rock; but immediately upon this repose thick beds of gneissoid rocks. Now gneiss, like granite, is composed of quartz, feldspar, and mica, and differs only in this-that the constituents have been broken up, assorted by water, and redeposited in regular layers. As we have different varieties of granitoid rocks, so we have corresponding varieties of gneissoid rocks, differing from the former only in being stratified. So general and so well recognized is this phenomenon, that Sir Roderick I. Murchison, an eminent geological authority, designates these lower strata beds of "fundamental gneiss." This occurrence of gneiss, every where reposing upon granite, is a most interesting and instructive fact, and confirms all that I have said of the denudation of the primitive islands, and the universality of the primitive sea.

But, though gneiss is generally the foundation stratum, we find abundance of other rocks either reposing upon the gneiss, or interstratified with it in the lower portions of the sedimentary series. Undoubtedly some of these have resulted from the impalpable powder to which long-continued attrition reduced some portions of the primitive granite, transported to the remotest and quietest portions of the ocean, and there allowed to subside. But we know also that others of the oldest strata associated with the gneisses have been the results of chemical agencies. This is one of the revelations of modern chemical geology, which no name has more adorned than that of Dr. T. Sterry Hunt, of the Geological Commission of the Dominion of Canada. According to Hunt and Logan, the limestones of this early period could have had no other than a chemical origin. Common limestone is composed, as every one knows, of carbonic acid and lime. Heat, as the manufacturer of lime

illustrates, expels the carbonic acid in the form of a gas. Under the high temperatures of the earliest periods, therefore, limestone could not exist. It has already been stated that all the carbon, sulphur, and chlorine in existence must, in those periods, have been represented by carbonic (CO2), sulphuric (SO3), and chlorhydric (HCl) acids, existing in a volatile state, mingled with the other gaseous constituents of the atmosphere. At the same time, all the silica of the globe, playing the part of an acid, would unite with the fixed elements, producing silicates of complex constitution -just such silicates as we actually find entering into the structure of the oldest portions of the earth's crust. The first rains which descended would be charged with the atmospheric acids just mentioned, which, attacking the solid silicates at a high temperature, would, as the analytical chemist knows, produce reactions resulting in the chlorids of calcium (CICa), magnesium (CIMg), and sodium (CINa), mingled with the sulphates of these bases (SO3KO, SO3NaO, SO3CaO, SO3MgO). The liberated silica (Si2O3) would separate, and would be chemically precipitated during the subsequent cooling of the waters, and would thus give rise to the enormous beds of quartz which we actually find among the very oldest strata, but nowhere else.

Among the other silicates originally formed is a family of minerals known as feldspars—very abundant, and containing, besides alumina, large percentages of either potash, soda, lime, or lithia, or two of these alkalies together. The decomposition of these feldspars-especially orthoclase, or potash-feldspar (Si2O3Al2O3KO)—must have taken place on an extensive scale. The result would be a clayey hydrate, called kaolin (Si2O3Al2O3) when pure, which became the basis of many clays and other argillaceous rocks like graphic and roofing slates. The remainder of the orthoclase would be in the form of silicates of potash (Si2O3KO) and

soda, which would remain in solution in the sea. But the carbonic acid of the atmosphere, having a more powerful affinity for these alkalies than the silica, would wrest them from combination with the silica, as already stated, and would form carbonates of potash (CO2KO) and soda (CO2NaO), while the silica would be added to the quartzose rocks of the globe. These carbonates, whether formed in the ocean or on the hill-sides, would, when transported to the ocean, find themselves confronted with chlorid of calcium (CICa), and probably other chlorids. Chlorid of calcium, carbonate of potash (CO2KO), and carbonate of soda (CO2NaO), brought face to face, would immediately enter into arrangements for an exchange of partners. Carbonic acid (CO2) would incontinently abandon potash (KO) and soda (NaO), and betake itself to calcium (Ca), changing its name, by the aid of a little oxygen, to "lime" (CaO), and forming a union known as carbonate of lime (CO2CaO). With equal celerity, chlorine (Cl), dispossessed of its calcium (Ca), would compensate itself by seizing upon potash (KO) and soda (NaO), and, after eliminating the oxygen. (O) in their constitution, would unite with potassium and sodium, forming chlorid of potassium (CIK) and chlorid of sodium (CINa). Thus all parties would be better satisfied, and each would abide in its appropriate place. Carbonate of lime (CO2CaO) refusing, for the greater part, to be dissolved in sea-water, would settle to the bottom and become limestone; while chlorid of sodium (CIN)—which is only the chemist's name for common salt"—remained in solution, and thus gave its characteristic salinity to the sea. Chlorid of potassium (CIK) also continues to exist in sea-water in smaller quantity.

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The diagram on the following page is intended to represent to the eye the chemical reactions above described. The symbols are familiar to the chemical reader; but they