At the moment when the earthquake commenced the two rivers Cuitimba and San Pedro flowed backwards, inundating all the plain now occupied by Jorullo; but in the regions which continually rose, a gulf opened and swallowed up the rivers. They reappeared to the west, but at a point very distant from their former beds.
This inundation reminds us on a small scale of the phenomena which attended the deluge of Noah.
Besides the deposits resulting from the partial deluges which we have described as occurring in Europe and Asia during the Quaternary epoch there were produced in the same period many new formations resulting from the deposition of alluvia thrown down by seas and rivers. These deposits are always few in number, and widely disseminated. Their stratification is as regular as that of any which belong to preceding periods; they are distinguished from those of the Tertiary epoch, with which they are most likely to be confounded, by their situation, which is very frequently upon the shores of the sea, and by the predominance of shells of a species identical with those now living in the adjacent seas.
A marine formation of this kind, which, after constituting the coast of Sicily, principally on the side of Girgenti, Syracuse, Catania, and Palermo, occupies the centre of the island, where it rises to the height of 3,000 feet, is amongst the most remarkable of the great Quaternary European productions. It is chiefly formed of two great beds; the lower a bluish argillaceous marl, the other a coarse but very compact limestone, both containing shells analogous to those of the present Mediterranean coast. The same formation is found in the neighbouring islands, especially in Sardinia and Malta. The great sandy deserts of Africa, as well as the argillo-arenaceous formation of the steppes of Eastern Russia, and the fertile Tchornozem, or “black earth” of its southern plains, have the same geological origin; so have the Travertines of Tuscany, Naples, and Rome, and the Tufas, which are an essential constituent of the Neapolitan soil.
The pampas of South America—which consist of an argillaceous soil of a deep reddish-brown colour, with horizontal beds of marly clay and calcareous tufa, containing shells either actually living now in the Atlantic, or identical with fresh-water shells of the country—ought surely to be considered as a Quaternary deposit, of even greater extent than the preceding.
We are now approaching so near to our own age, that we can, as it were, trace the hand of Nature in her works. Professor Ramsay shows, in the Memoirs of the Government Geological Survey, that beds nearly a mile in thickness have been removed by denudation from the summit of the Mendip Hills, and that broad areas in South Wales and the neighbouring counties have been denuded of their higher beds, the materials being transported elsewhere to form newer strata. Now, no combination of causes has been imagined which has not involved submersion during long periods, and subsequent elevation for periods of longer or shorter duration.
We can hardly walk any great distance along the coast, either of England or Scotland, without remarking some flat terrace of unequal breadth, and backed by a more or less steep escarpment—upon such a terrace many of the towns along the coast are built. No geologist now doubts that this fine platform, at the base of which is a deposit of loam or sandy gravel, with marine shells, had been, at some period, the line of coast against which the waves of the ocean once broke at high water. At that period the sea rose twenty, and thirty, and some places a hundred feet higher than it does now. The ancient sea-beaches in some places formed terraces of sand and gravel, with littoral shells, some broken, others entire, and corresponding with species in the seas below; in others they form bold projecting promontories or deep bays. In an historical point of view, this coast-line should be very ancient, though it may be only of yesterday in a geological sense—its origin ascending far beyond written tradition. The wall of Antoninus, raised by the Romans as a protection from the attacks of the Caledonians, was built, in the opinion of the best authorities, not in connection with the old, but with the new coast-line. We may, then, conclude that in a.d. 140, when the greater part of this wall was constructed, the zone of the ancient coast-line had attained its present elevation above the actual level of the sea.
The same proofs of a general and gradual elevation of the country are observable almost everywhere: in the estuary of the Clyde, canoes and other works of art have been exhumed, and assigned to a recent period. Near St. Austell, and at Carnon, in Cornwall, human skulls and other relics have been met with beneath marine strata, in which the bones of whales and still-existing species of land-quadrupeds were imbedded. But in the countries where hard limestone rocks prevail, in the ancient Peloponnesus, along the coast of Argolis and Arcadia, three and even four ranges of ancient sea-cliffs are well preserved, which Messrs. Boblaye and Verlet describe as rising one above the other, at different distances from the present coast, sometimes to the height of 1,000 feet, as if the upheaving force had been suspended for a time, leaving the waves and currents to throw down and shape the successive ranges of lofty cliffs. On the other hand, some well-known historical sites may be adduced as affording evidence of the subsidence of the coast-line of the Mediterranean in times comparatively modern. In the Bay of Baiæ, the celebrated temple of Serapis, at Puzzuoli, near Naples, which was originally built about 100 feet from the sea, and at or near its present level, exhibits proofs of having gradually sunk nineteen feet, and of a subsequent elevation of the ground on which the temple stands of nearly the same amount.
So, also, about half a mile along the sea-shore, and standing at some distance from it, in the sea, there are the remains of buildings and columns which bear the name of the Temples of the Nymphs and of Neptune. The tops of these broken columns are now nearly on a level with the surface of the water, which is about five feet deep.