and sand; the cementing material was, of course, derived from the oxidation of the iron or steel knife-blades.
Of the rapidity with which the aggregation and consolidation of loose materials take place at the bottom of the sea, a striking proof was afforded in Capt. Dickenson's gallant and successful operations, by means of a diving-bell, to recover the treasures of a richly-laden vessel,—the "Thetis,"—which was wrecked and sunk, in twenty fathoms water, off Cape Frio, to the east of Rio de Janeiro, in a bay bounded by granite cliffs. The floor of the ocean-bed was found to be composed of micaceous and quartzoze sand, consolidated into what may be termed regenerated granite; the super- incumbent pressure of the water, aided by the huge materials of the wreck of the frigate, and enormous blocks of granite, which, under the influence of the swell, acted with tremendous momentum, like the steam-hammers of a foundry, in a few weeks compressed the sand, wood, and iron, and the gold and silver coins, into solid masses of rock, which were broken up with difficulty to extract the impacted dollars.
It is unnecessary to adduce other examples of the nature and extent of the deposits which are in progress at the bottom of the present seas; but in passing to the next topic, I would solicit particular attention to the fact, that vast subaqueous accumulations of the relics of man and his works, must have been going on for ages, and imparting a character to the strata of the human epoch, of which no traces whatever are observable in the ancient formations.
II.—On the Occurrence of the Remains of Man and Works of Art in modern superficial Deposits.
From the phenomena thus briefly considered, the archæologist will be prepared to meet with the remains of man and his works in deposits which, though but of recent origin in a geological sense, are of immense antiquity in relation to human history and tradition; suggesting the interestingquestion as to the remoteness of the period to which our present retrospective knowledge of the existence of mankind extends. In this division of the subject, my observations will be restricted to a few illustrations from the historic period.
Coins.—Coins, from their durability, and the facility with which the accomplished numismatist can determine their date, even when the inscription is obliterated, are the most
