consider these as necessaries of life; inquiries were therefore made to Signor Gemmellaro, "in the hope," says Sir C. Lyell,' "that his local knowledge of Etna might enable him to point out some crevice or natural grotto on the mountain, where drift snow was still preserved. Nor were they disappointed; for he had long suspected that a small mass of perennial ice at the foot of the highest cone was part of a large and continuous glacier covered by a lava current. Having procured a large body of workmen, he quarried into this ice, and proved the superposition of the lava for several hundred yards, so as completely to satisfy himself that nothing but the subsequent flowing of the lava over the ice could account for the position. of the glacier." This interesting spot is near the Casa Inglese, on the south-east side of the cone.

Regarding the probable origin of this phenomenon, Sir C. Lyell goes on to observe :-"We may suppose that, at the commencement of the eruption, a deep mass of drift-snow had been covered by volcanic sand showered down upon it. before the descent of the lava. A dense stratum of this fine dust mixed with scoriæ, is well known to be an extremely bad conductor of heat; and the shepherds in the higher regions of Etna are accustomed to provide water for their flocks during summer, by strewing a layer of volcanic sand a few inches thick over the snow, which effectually prevents the heat of the sun from penetrating." On the authority of Lieutenant Kendall,2 Deception Island, in New South Shetland, is chiefly composed of alternate layers of ice and volcanic ashes.

236. The iceberg is the creation of many ages; originally a prodigious glacier reposing in the valley of some polar mountain, it has been loosened from its hold and tumbled in the ocean. Dreaded by the navigator, it floats a fantastic and majestic island. In Spitzbergen and Greenland the iceberg is seen in all its grandeur and its terror. "Frost," says Pennant, "sports with these icebergs, and gives them majestic as well as singular forms. Masses have been seen

1

Princip. of Geol. vol. ii. p. 233.

Jour. Roy, Geogr. Soc. i, 64.

Scoresby, Arct. Reg. vol. i.; Latta,-Ed. Phil. Jour. iii.

assuming the shape of a gothic church with arched windows and doors, and all the rich drapery of that style, composed of what an Arabian tale would scarcely dare to relate, of crystals of the richest sapphirine blue; tables with one or more feet; and often flat-roofed temples like those of Luxor on the Nile, supported by transparent columns of cerulean hue, float by the spectator."

Captain Horsburgh mentions having met with icebergs like church spires, from 250 to 300 feet high, off the Cape of Good

Iceberg seen off the Cape of Good Hope, April 1829, in S. lat. 39° 13', and E. long. 48° 46', by Captain Horsburgh.

Hope, in sea where there was no sounding. We have the testimony of another witness to a similar fact,-"Islands of ice," says Dalrymple," "have been seen sometimes, though rarely, by our ships in doubling the Cape." Captain Weddell' fell in with one in the antarctic ocean, which rose to a height of 180 feet, and was cracked from the water-mark to the summit which overhung the rest. "We had," he says, "the appalling sight of the overhanging mass immediately over our quarter-deck, with the fearful sensation that if our masts came in contact with it, the projecting part would fall upon us and sink both vessels. Our escape was caused solely by our having a large piece of ice between us and the iceisland, which prevented us touching it." This navigator, on February 10. 1823, in S. lat. 64° 15' and W. long. 30° 46', 2 Mem. on Southern Ocean, p. 17.

1 Phil. Trans. 1830.

met with ice so incorporated with black earth that it was mistaken for terra firma. This circumstance recals to mind an interesting observation of Sir J. C. Ross, on his first antarctic voyage, illustrating the drifting of stones through this medium. It was in the year 1839, when an iceberg was discovered with a block of rock imbedded in the ice, in S. lat. 61°, and 1400 miles from the nearest known land, though perhaps not more than 100 from land yet unseen. The portion visible was about 12 feet high and 6 wide, and nearly 100 feet above the water mark.' In Davies' Straits, where there is deep water, icebergs have been met with having an area of nearly six square miles, and rising to the altitude of about 600 feet. Near to Whale Island, in this strait, in N. lat. 69°, Sir J. C. Ross' met with icebergs rising 200 feet above the ocean, and having a proportionate bulk, in June 1848. As it may be experimentally shown, that floating ice sinks seveneighths of its entire mass under water, it follows that an iceberg, rising only a few fathoms above the ocean, must be immense. Sir John Franklin, however, observes, that these masses of ice are frequently magnified to an immense size, through the illusive medium of a hazy atmosphere, and on this account their dimensions have been sometimes exaggerated by voyagers. It should be remembered too, that icebergs are often stranded; thus, Sir John Ross saw several aground in Baffin's Bay, in water of 260 fathoms. One there, was computed to weigh 1,292,397,673 tons; its dimensions were 51 feet high, 12,507 feet long, and 11,067 feet broad,(1 mile lineal=5,280 feet). Captain Beechey computed the weight of one of small size which he saw to fall from a glacier in Spitzbergen, at 421,660 tons. Graah,' the recent Danish voyager, whose success in reaching a high latitude under the most unaccountable want of every requisite for such an expedition, is beyond praise, with a slender boat covered with skins, and women as his rowers, with inadequate food, and

1

4

Voy. of Discov.; Jour. of Royal Geogr. Soc. vol. ix. 526, 529.

2 Letter dated 29th June 1848,-Record of Sept. 21. 1848.

3 Narrative, 3d ed. vol. i. p. 18.

Undersögelses-Reise til Östkysten af Grönland, 1828-31: Copenhag. 1832,

Macdougall.

sometimes none at all,-with nothing to administer relief when sick, with little more than his instruments for determining his geographical position,—and all this in the 19th century, by an enlightened government !-this enterprsing officer estimated the magnitude of an iceberg on the east coast of Greenland, at a height of 120 feet, 4000 feet in girth, and containing 900,000,000 cubic feet.

The Great Western steam-ship, during its transatlantic voyage in April 1841, passed within sight of 300 icebergs, the largest of which was nearly 100 feet in height, and three fourths of a mile in length; and was close upon an ice island above 100 miles long, running from E. to W., between lat. 42°–43°, and long. 48°-50°. The thermometer fell to 28° F., and the temperature of the ocean to 25°, in the immediate vicinity of the icy mountain. Upon the 19th of the same month, the William Brown of Philadelphia, was lost by striking on an iceberg in N. lat. 43° 30', and W. long. 49° 39'. In March 1826, the Ajax, in N. lat. 44° 30', and W. long. 42° 44', found herself for 300 miles close to ice-islands and icebergs; once they were so near, that the captain and part of the crew walked upon the ice.1 On the 4th of March 1847, during the homeward passage of the Cambria, ice was met with in very large blocks, which choked the wheels and injured the paddle-boxes. On May 21st, in the same year, the Eulalia was cut down by an iceberg, in lat. 42°, and long. 52°; twenty persons perished. In the summer of 1848, in N. lat. 48°, and W. long. 49°, the Blonde of Greenock met with an iceberg a mile in length and 600 feet in height. Besides the cold which is experienced in the neighbourhood of these icebergs, Foery' observes that they "give to the winds which blow a harsh and chilling influence."

237. Icebergs are rarely, if ever, met with between lat. 40° N. and 36° S.; one, however, is said to have been observed off Antigua. In the Atlantic, the normal longitudinal limits of icebergs are between W. long. 42° and 52°; once in 1817,

3

1 Clim. of Unit. States.

Unit. Serv. Jour. ii. 716-720; Quart. Rev. No. 36.

3 Unit. Serv. Jour. 1829, ii. 718, note.

ice was seen to the east of the former parallel, in long. 33°. Von Buch' observes that in Europe, the most southern part where a glacier descends to the sea-level, and thereby generates the iceberg, is in Norway, in N. lat. 67°; in the southern hemisphere, however, this point is met with, according to Darwin, in S. lat. 46° 40°.

2

238. Icebergs are known to split into fragments without an apparent cause, accompanied by a sound like that of thunder; and in the case of the collision of two, with the production of light. This phenomenon M. Becquerel attributes to electricity. A parallel phenomenon was observed in December 1819, on the the descent of the Weisshorn glacier upon the village of Randa; when the ice and snow struck the inferior mass of the glacier, during the night, a light flashed, and almost instantly disappeared.3 Icebergs are observed to present different colours and shades of blue. Scoresby' mentions, that when newly fractured, the edges glisten with a greenish-blue, approaching to emerald-green, but, when long exposed, they exhibit the appearance of a marble cliff.

239. The curious circumstance of the iceberg being capped with mist is sometimes witnessed. This is owing to the evaporation from its surface, and the low temperature of the surrounding air, for we have mentioned that both the atmosphere and ocean indicate a decline of heat in the vicinity of an iceberg. At other times the entire iceberg is enveloped by the fog, and then becomes one of the most formidable weapons of destruction to the vessels navigating the polar

seas.

240. We would conclude this portion of our subject with a brief notice of some of the physical properties of ice not already described. Its specific gravity is less than that of water, and its refractive power is 1.3 below that fluid. When slowly conglaciated, it assumes the form of regular crystals. Haüy supposed the primary form to be octahedral; and Scoresby," Romé de Lisle, and D'Antic,' sometimes found crystals of

6