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NATURE 
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reflection from the red-hot sides of the crater itself, and from the 
surface of the molten lava below. 
The chemical composition of the gasiform emanations from 
volcanoes proves that they are in greater part incombustible, and 
therefore does not support the idea that the body of such a 
column of yapour and gases could be in. flames, 7¢., actually 
burning. On the outside of the column, however, innumerable 
brilliant scintiliations of a bluish colour are frequently seen, due 
to particles of sulphur taking fire as they come in contact with 
the outer air, and patches of melted sulphur are splashed about, 
burning brightly as they fall through the air on to the slopes of 
the cone. ‘The emission or belching forth, as it has been called, 
of the gaseous matter with its accompanying red-hot ashes and 
scoriz, is more an intermittent than a cont’nuous operation. 
When an eruption is at its height the spasmodic puffs or blasts 
are jerked out at intervals of but a few seconds, attended by a 
terrific roaring or bellowing noise difficult to describe in words. 
The buried cities of Stabia, Herculaneum, and Pompeii, 
covered up in parts to the depth of 100 feet by the ashes of 
Vesuvius, are ocular proofs of the vast quantity which can be 
sent out of a volcanic vent during an eruption, The volcano of 
Sangay, in Ecuador, in constant activity since 1728, has buried 
the country around it to a depth of 400 feet under its ashes, and 
a French geologist has estimated that in the course of only two 
days the volcano of Bourbon has thrown out no less than 300,000 
tons of volcanic ashes, The immense distances to which these 
my be transported by the winds is no less surprising ; the ashes 
of Vesuvius, in the eruption which buried Pompeii, darkened the 
sun at Rome, and were carried as far as Syria and Egypt ; those 
from San Vincent, in 1812, are reported to have made the sky 
as dark as night in the Barbadoes ; and in Iceland, in 1766, the 
air became so charged with ashes for a distance of 150 miles 
around Hecla, that even the brightest light could not be dis- 
tinguished at a few yards. 
Amongst the still active volcanoes we meet with some whose 
craters are several miles in diameter, encircled by precipitous 
sides rising to even a thousand feet above the bottom of the crater 
when at rest, which, as in the Sandwich Islands, may contain 
reservoirs, or rather lakes of liquid Java, two to four miles across, 
and at times send forth rivers of molten stone several miles in 
breadth, extending their fiery inundation to a distance of even 
forty miles from the crater whence they issued. In the eruption 
of Hualalai, in 1801, a lava current, after reaching the coast, 
poured out such volumes of melted matter as to fill up a bay 
some twenty miles deep, and in its place extend a headland some 
three or four miles farther into the sea. The rate at which these 
rivers of molten stone flow is a very varying one ; in 1805 the 
lava current from Vesuvius is said to have run down the first 
three miles in four minutes, yet only completed its total distance 
of six miles in three hours ; and in 1840 that from Mauna-Loa | 
advanced no less than eighteen miles in two hours ; whilst on the 
other hand it is recorded that during the eruption of Etna, 
which commenced in 1614, and continued many years, the lava 
stream only completed a distance of six miles in ten years, not- 
withstanding that all this time it was seen to be in slow but 
almost imperceptible motion ; during the eruption of this volcano 
in 1865, I found, however, that at the edge of the current the 
rate of motion varied from 15 to 120 feet per hour according to 
local circumstances ; in the centre of the stream the lava was 
evidently still more rapid in its movements. 
The entire mass of a lava stream often advances, even when 
to the eye it would appear to have become quite solid ; upon 
my throwing a heavy stone on to the top of a lava current so far 
‘consolidated that the stone merely fixed itself into the surface 
without sinking deeper, it was seen that the stone moved along 
with the lava whicl: otherwise looked as if stationary. The 
surface of this lava consolidated and cooled with a:most in- 
credible rapidity, so much so that, notwithstanding the protesta- 
tions of my guides, I walked over lava currents when, a: the same 
time, the fiery stream still flowing below could be distinctly 
seen through the cracks in the crust over which I passed. 
On this occasion also the stems of the pine-trees in the forest 
which was destroyed by this eruption were converted into char- 
coal as high as the lava reached, but the upper portions of the 
trees then toppled over, and renained in an almost unaltered 
and uncharred condition on the top of the lava current which 
had so quickly cooled. ‘The crust which forms on the top e 
lava when cooling, being an excellent non-conductor, acts so 
efficiently in preventing further escape of heat, that we find 
streams of lava requiring many years and even ages to become 
quite cold. Dolomier relates that the lower part of the Ischia 
lava of 1301 was still hot in the year 1785. 
When, owing to the descriptions of the ground around yol- 
canoes, the water from springs, rivers, lakes, or the sea itself, is 
brought into contact with the heated mineral matter below, we 
have the production of the so-cl ed mud volcanoes or of fissures 
sending forth torrents of heated mud and water, and often, to the 
great surprise of the inhabitants, throwing out numbers of fishes 
which had lived previously in these sources. The Geysers of Ice- 
land are somewhat similar phenomena, but on the present occa- 
sion time will not permit these subjects being treated in detail. 
Whilst some volcanoes like Stromboli, the lighthouse of the 
Mediterranean, as it was called by the ancients, have continued 
in incessant activity from the oldest historical periods down to 
the present day, the cruptions of others are only known to have 
taken place at long intervals. Vesuvius, although imagined by 
Strabo to have had a volcanic origin, was not known even by 
tradition to have ever been in eruption until the year 79, when 
Pompeii was overwhelmed by it. Since that time, however, up 
to the present date, it has given ample proof of its volcanic 
activity, yet its history shows several intervals of a century, and 
one of more than two centuries, in which 1:0 eruption took place. 
No outbreak of the volcano Sangay in Ecuador is recorded before 
1728, since which year it has been in continued activity, and 
Krabla in Iceland also remained at rest for several huntred years 
before 1724. In fact, it may be safely affirmed that it is quite 
impossible for us to know whether any volcano at all is entitled 
to be regarded as really extinct. Even for ages after the last 
outburst of lava, it is found that smoke and acid vapours continue 
to be given off from most volcanic rents, and the extraction of the 
sulphur found in the craters and sublimed into the fissures 
around dormant volcanoes, forms in many cunntries an important 
branch of industry. 
Although, as yet, I have confined my remarks altogether to 
terrestrial volcanoes, it must not be supposed that the depths of 
the sea are exempt from such visitations, and in the last few years 
we have had several prominent examples to the contrary in dif- 
ferent parts of the world. Submarine volcanoes were well known 
to the ancients ; Pliny and older writers refer to those in the 
Mediterranean which threw up the islands of Delos, Rhodes, 
Anappe, Nea, &c. In the Cyclades very curious examples have 
occurred, both in very ancient and in the most recent times. Of 
these islands, Therasia is recorded to have been formed in the 
third century B.C., as also somewhat later in the same century 
the island of Thera, now called Santorin ; subsequently Hiera, 
gi B.c., and then Thea, A.D. 19, appeared, which last two 
were, in 726, united by an eruption, and together formed the 
present island of Kaimeni, In 1575 a smaller island called Little 
Kaimeni showed itself, around which, in 1650, numerous other 
islets were thrown up, which subsequently became united to Little 
Kaimeni during the eruptions, which continued from 1707 to 
1812, when the island, thus increased in size, became known 
as New Kaimeni, Finally, the last eruption (still going on), 
which commenced 28th January, 1866, presented us, on the 2nd 
February, with a new island, now called King George’s Island, 
from the present King of Greece, which, according to the latest 
accounts, still continues to increase in size. Numerous other 
examples might be cited, but I shall only mention the island of 
Johanna Bogoslawa, in Alaska, which, although it only first 
showed itself above the water in May 1796, had, in 1806, in- 
creased so as to be an immense volcanic island, the summit of 
which was then elevated to no less than 3,000 feet above the 
level of the sea. 
The volcanic products thus forced out under the sea present, 
as might be expected, a very different aspect from that of the 
ashes, scoria, and lava from terrestrial volcanoes ; the molten lava 
coming in contact with the water is at once broken up into frag- 
ments, coarser or finer, in proportion to the greater or less cooling 
power of the water in immediate contact with them, and often in 
great part instantly converted into fine mud, of a greyish colour 
when formed from prachytic lava, but more commonly of a 
chocolate or other dark tint, and much denser when produced 
from the more prevalent pyroxenic lava. Beds of this character, 
spread out by the action of the sea, often enclosing shells, fish, 
and other organic remains, become in time consolidated and 
upheaved, and as they often presentlan appearance much resem- 
bling ordinary {volcanic rocks, they have frequently puzzled 
geologists, who at first found a difficulty in explaining the presence 
of such fossils in rocks apparently of igneous origin. 
Many writers on this subject hold to the belief that volcanoes 
