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It is not true, as was formerly supposed, that all granites, together with the crystalline or metamorphic strata, were first formed, and therefore entitled to be called "primitive," and that the aqueous and volcanic rocks were afterwards superimposed, and should, therefore, rank as secondary in the order of time.
In those days the rocks which are now the very bones and sinews of our mother earth her granites, her porphyries, her basalts, her syenites were melted into a liquid mass.
And this concert comes always from above. Owls, ospreys, screech-owls, all the different kinds of birds, with hooked beaks and round eyes, and silken wings that enable them to fly noiselessly, have their homes amongst the granites massively upheld in the air; and they are celebrating now, each after its own fashion, the nocturnal festival.
The central plateau consists of ancient crystalline rocks with granites overlain by unfossiliferous sandstones and conglomerates considered to be of Palaeozoic age. The outcrops are largely hidden under laterite. The median zone is composed largely of crystalline rocks with granites and some Palaeozoic unfossiliferous rocks. The littoral zone contains the only fossiliferous strata.
Farther on, when we have left behind this region of tombs, the granites alone litter the expanse of sand, granites to which the usury of centuries has given the form of huge round beasts. In places they have been thrown one upon the other and make great heaps of monsters. Elsewhere they lie alone among the sands, as if lost in the midst of the infinitude of some dead sea-shore.
But to admit the "Plutonic" origin of such widespread formations was practically to abandon the Neptunian hypothesis. So gradually the Huttonian explanation of the origin of granites and other "igneous" rocks, whether massed or in veins, came to be accepted. Most geologists then came to think of the earth as a molten mass, on which the crust rests as a mere film.
The partial ascent of the mighty Sharr gave an admirable study of the mode in which the granites have been enfolded and enveloped by the later eruptions of trap.
They were great destroyers of the queen city, were these same Persian soldiers. To break up the obelisks and the colossal statues they conceived the plan of scorching them by lighting bonfires around them, and then, when they saw them burning hot, they deluged them with cold water. And the granites cracked from top to base.
All the various kinds of granites which constitute the Plutonic family are supposed to be of igneous or aqueo-igneous origin, and to have been formed under great pressure, at a considerable depth in the earth, or sometimes, perhaps, under a certain weight of incumbent ocean.
The Uspallata chain corresponds in geographical position, though on a small scale, with the Portillo line; and its clay-slate formation is probably the equivalent of the mica-schist of the Portillo, there metamorphosed by the old white granites and syenites.
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