buted to lavas and other plutonic rocks, during their emission or elevation under extreme pressure. He produced examples from the ribboned trachytes and pearlstones of Italy, Hungary, and Mexico. He considers gneiss to be granite elongated by a powerful lateral squeeze, probably at the time of its expulsion; and mica-schist to be the extreme result of the same action upon the lateral bands or selvages of the extruded mass or great dyke. This he thinks a more probable origin than the usual metamorphic theory of the melting and reconsolidation of sedimentary strata, though the one does not wholly exclude the other. At all events he considers the evidence presented in the peculiarities of texture, structure, and position of the laminated crystalline rocks to be conclusive as to their having been squeezed, flattened, and drawn out in the direction of their upcast, and attributes this process to the same elevatory movements which have thrust them up, and often forced them into wrinkled foldings on the grandest as well as on the most minute scale. To this same reärrangement of their crystalline plates or flakes under pressure he attributes also their lamellar cleavage. He refers to Mr. Sorby's recent papers and experiments on slaty cleavage as confirming these views. The paper ends by recommending the more earnest study of the dynamics of geology, which have in this country been perhaps of late years somewhat neglected.

11. HERCULANEUM AND POMPEII.-We have above described the phenomena attendant on the modern paroxysms of Vesuvius: but this celebrated mountain is invested with surpassing interest, from the wonderful preservation of the cities, which were overwhelmed by its firstrecorded eruption, in the seventy-ninth year of the Christian era.

In the words of an eloquent writer, "After nearly seventeen centuries had rolled away, the city of Pompeii was disinterred from its silent tomb,-all vivid with undimmed hues,-its walls fresh, as if painted yesterday,-not a tint faded on the rich mosaic of its floors,-in its Forum the half-finished columns, as left by the workman's hand,—before the trees in its gardens the sacrificial tripod,-in its halls the chest of treasure,—in its baths the strigil,-in its theatres the counter of admission,-in its saloons the furniture and the lamp,-in its triclinia the fragments of the last feast,

in its cubicula the perfumes and the rouge of faded beauty, -and everywhere, the skeletons of those who once moved the springs of that minute yet gorgeous machine of luxury and of life."*

From the description of the catastrophe by an eye-witness, it appears that this outburst of Vesuvius was marked by a terrific eruption of ashes and scoriæ, which, borne upwards by vapours, rose in an immense column, and is described by the younger Pliny, in his letter to Tacitus, as resembling a lofty pine spreading out at its summit into wide shadowing branches and then followed total darkness, occasioned by the descent of this overwhelming cloud of volcanic matter, which completed the destruction of the devoted cities, and buried Herculaneum, Pompeii, and Stabiæ beneath an accumulation of ashes, cinders, and scoriæ, to a depth of from sixty to one hundred and twenty feet.

:

No traces have been perceived of lava-currents or of melted matter; the various utensils and works of art, as you may observe in the Pompeiian lamps, vases, beads, and

* Sir E. Bulwer Lytton's "Last Days of Pompeii."

†The elder Pliny, who, at the time of this outburst of Vesuvius, held the command of the Roman fleet, stationed at Misenum-a cape or headland about twice the distance westward from the volcano as the city of Naples,-in his anxiety to obtain a nearer view of the phenomenon, fell a victim to the sulphurous vapours: and his nephew, the younger Pliny, who remained with the fleet at Misenum, has left a graphic description of the awful scene in his letters to Tacitus. He states, that a dense column of vapour was first seen arising vertically from Vesuvius, and which spread itself out laterally, so as to resemble the head and trunk of the Italian pine-tree. This black cloud was occasionally pierced by flashes of fire as vivid as lightning, and the whole atmosphere sud denly became darker than night. The eruption burst forth with such amazing force, that ashes fell even upon the ships at Misenum, and in such quantities as to cause a shoal in one part of the neighbouring sea. In the mean time, the ground rocked terribly; and the sea re ceded so far from the shore, that many marine animals were left exposed on the dry sand,

instruments in the British Museum, exhibit no appearance of having been exposed to the action of fire. Even the delicate papyri appear to have sustained more injury from the effects of moisture and exposure to the air, than from heat; for they contain matter soluble in naphtha, and are in fact

The site of Pompeii is marked by the long line of embankments in the middle distance, formed by the ashes thrown out of the excavations. The River Sarnus is seen on the left. (From Sir W. Gell's Pompeiana.)

peat in which bituminization has commenced.* In Pompeii, the sand and stones are loose and unconsolidated; but in Herculaneum, the houses and works of art are imbedded in solid tuff, which must have originated either from a torrent of mud, or from ashes moistened by water. Hence statues are found unchanged, although surrounded by hard tuff, bearing the impressions of the minutest lines. The beams of the houses have undergone but little alteration, except that they are invested with a black crust. Linen and fishingnets, loaves of bread with the impress of the baker's name; Dr. Macculloch.

even fruits, as walnuts, almonds, and chestnuts, are still distinctly recognisable. The remarkable preservation, for nearly two thousand years, of whole cities, with their houses, furniture, and the most perishable substances, imbedded in volcanic matter, may be compared to those geological events by which the forests of an earlier world, and the remains of the colossal dragon-forms which inhabited the ancient lands and waters, have been accumulated beneath the deposits of innumerable ages.

12. CONSERVATIVE EFFECTS OF LAVA-CURRENTS.-Although no vestiges of animals or plants are likely to be found in volcanic products that have been in an incandescent state, yet so slow is the conducting power of many earths, that beds of shells and vegetable remains may be overflowed by streams of molten lava without injury, if protected by even a thin covering of sand or other non-conducting material. In like manner the ancient basaltic lavas have burst through and overwhelmed sedimentary strata, and yet the most delicate animal and vegetable substances remain uninjured; transmuted, indeed, into stone, but still retaining their original structure. Thus, in the eocene (?) beds of Glarus, although the rock has been converted into slate by intense heat, yet the fishes remain (p. 366); the strata of Monte Bolca, though capped with basalt, yet swarm with ichthyolites (p. 269); the fiery currents of Auvergne have flowed over the lacustrine limestones, and still vestiges of insects, serpents, and quadrupeds are preserved (p. 277); the tertiary forests of the Andes, which grew on beds of lava, now lie buried beneath subsequent volcanic eruptions of prodigious thickness (p. 289); and bones either of the Dodo or of the Solitaire are found imbedded in sandstone covered by lava of recent origin (p. 130).

A very remarkable circumstance is mentioned by Sir. C. Lyell, the preservation of a bed of ice, beneath a stream of incandescent lava. The intense heat experienced in the

south of Europe during the summer and autumn of 1828 caused the usual supplies of ice entirely to fail. Great distress was consequently felt from the want of a commodity regarded in those countries rather as an article of necessity than of luxury. Etna was, therefore, carefully explored, in the hope of discovering some crevice or natural grotto on the mountain where drifted snow was still preserved. Nor was the search unsuccessful; for a small mass of perennial ice at the foot of the highest cone was found to be part of a large continuous glacier covered by a sheet of lava. The ice was quarried, and the superposition of the lava ascertained to continue for several hundred yards; unfortunately, the ice was so extremely hard, and the removal of it so expensive, that there is no probability of the operations being renewed.* Sir C. Lyell explains this apparently paradoxical fact by supposing that a deep mass of drift-snow was covered by a layer of volcanic sand, which is an extremely bad conducter of heat; and thus the subsequent liquid lava might have flowed over the whole without affecting the ice beneath, which at such a height (ten thousand feet above the level of the sea) would endure as long as the snows of Mont Blanc, unless melted by volcanic heat from below.

13. ORGANIC REMAINS IN LAVA.-The silicious shields or frustules of Infusoria are often found as a component part of volcanic ash and tuff, both of ancient and modern origin,† and were probably derived from the subterranean pools or lakes; as in the case of the showers of fishes which occasionally descend during a volcanic eruption. Infusorial

* Principles of Geology, vol. ii. pp. 124-126, 9th edit. p. 412. + Prof. Ehrenberg has published several notices of this phenomenon in the Journal and Transactions of the Berlin Academy of Sciences; and complete illustrations are given in his magnificent " Mikrogeologie,” fol. 1855.

Humboldt's Cosmos, vol. i. p. 230. A putrid fever which prevailed in 1691, in Ibarra, north of Quito, was ascribed to the decomposition of the quantity of dead fish ejected from the volcano of Imbaburu.