between Archceology and Geology. 241 



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," 

 — w^hich 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 quartzose 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 tremen- 

 dous 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 archaeo- 

 logist will be prepared to meet with the remains of man and 

 his works in deposits which, though but of a recent origin in 

 a geological sense, are of immense antiquity in relation to 

 human history and tradition ; suggesting the interesting 

 question 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 

 instructive relics of human art that occur in the mineral 



VOL. L. NO. C. — APRIL 1851. Q 



