Page:A Treatise on Geology, volume 1.djvu/342

 326 Good Hope; the elevated terraces of shells on the coast of Valparaiso, and on the plains of Patagonia; the coral masses in the interior of Antigua; the shelly beds of Barbuda; the Keys or sand islands on the coast of Florida; and the sandy portion of the Atlantic plain which borders the United States (Rogers, in Brit. Assoc. Reports); for it seems difficult not to recognise, in these and many other examples, proof of the very great extent to which the level of land and sea has been and still is locally variable.

From what has been already stated, it may be inferred that, since the completion of much of the tertiary system of strata, the northern zones of Europe and America have been deeply submerged below an ocean which in several parts at once, perhaps in all parts at different times, was traversed by arctic currents, if it had not perpetually a boreal character. This ocean has been repelled by the uprising of the land, and the ancient deposits remain, in part, on the now dry ground. Only in part, for by the agitation of the sea at the uprising, and the subsequent action of atmospheric forces, much of the old sea bed has been worn away and removed. The raised beaches are some of the littoral parts of this bed. They are not now necessarily at one constant height above the sea, for the upward movement may not have been to the same vertical amount at different points; nor have they necessarily one mineral or structural character; nor must they necessarily contain all the same shells or other organic reliquiæ. In this latter particular they may vary, not only because of any original local diversity of the fauna, at one epoch, but also because the beaches may have been raised at different times, or from other causes may contain the remains of different periods.

Under these circumstances it may appear hopeless to determine, amongst the raised beaches, more than very vague relations to geological time. We know that they belong to a very late class of tertiary formations, and that their antiquity is such as to put them far beyond the scope of modern deposits.