Mountains.

Volcanoes.

base towards the east, extending from Thrándar jökull to
Langanes, and with its apex at Baula. This plain is a com-
plete desert, covered with vast lava beds, as the Odatha Hraun,
with extensive tracts of black sand, as the Stori and Sprengi-
sandur, or with rock and mud sprinkled with lichen and moss in
sheltered hollows, as the Arnarvatn Heithi. This wilderness is
traversed by three main routes, the Thvídægravegr, the Kjalvegr,
and the Sprengisandur way.

These two triangles form a parallelogram including 20,000
square miles of country perfectly barren and uninhabitable, and
only partially explored. It has been estimated that but 4,000
square miles of Iceland are inhabited; the rest of the country is
a chaos of ice, desert, and volcanoes.

The mountains of Iceland are divided into two classes, the fells and the jökulls. The former are, for the most part, free from snow during the hottest portion of the summer; but the latter are shrouded in eternal ice. The conformation of the mountains is very varied. The jökulls have generally rounded heads of ice resting on abrupt flanks of rock. This ice is formed by the pressure of enormous superincumbent masses of fresh snow, converting this at any depth to blue glacier ice. Sections such as may be seen in Kaldidalr and on the flanks of Eireks jökull give to these beds a thickness of about one hundred feet.

As there is a constant thrust from the highest points of the
mountain exerted upon the ice, it moves slowly over the rocky
ledges, and breaks off in crags of green ice, which fall to the
bottom of the precipices with a roll like thunder. On the south
of the Vatna and Myrdals jökulls, where the mountains shelve
gently to the sea, glaciers resembling those of Switzerland may
be seen, but they are entirely absent from the centre of the
island. The principal jökulls are-the Orofa, height 6,241
feet; Eastern Snæfell, 5,160 feet; Eyjafjalla, 5,432 feet; Her-
thubreith, 5,290 feet; and Western Snæfell, 4,577 feet. The
latter has alone been surmounted. Mr. Holland, in 1861,
ascended to a great height on the Orofa, but did not gain the
summit. The fells are mountains of different character; they
may be rounded at top, but they support no ice-fields, and are
inferior in elevation to the jökulls. In shape they vary con-
siderably some are saddlebacked, others conical or pyramidal.
Some, as well as the jökulls, are volcanoes, and have often
caused much havoc. Hekla, for instance, is a fell, whilst the
terrible Skapta is a jökull.

The most violent volcanic action seems to lie in a band from
Krafla to Reykjanes.

In this belt lie the following principal volcanoes-Krafla and Leirhuukr, both near Myvatn; Trölladyngja, in the Odathahraun; Skapta and Orofa, the westernmost points of the enormous Vatna jökull, Katla or Kötlugjá, and its twin mountain Myrdals jökull, and Hekla.

The total number of recorded eruptions is:-
Eldborg, date uncertain.

894. Katla erupted for the first time.

934. Katla for the second time.

1000. Katla again (the date is not certain).

1004. Hekla for the first time.

1029. Hekla for the second time.

1104-5. Hekla for the third time.

1113. Hekla for the fourth time.
1150. Trölladyngja for the first time.
1157. Hekla for the fifth time.

1188. Second eruption of Trölladyngia.

1204. Hekla. Sixth eruption.

1210. At sea, near Reykjanes.

1219. At sea, near Snæfells jökull.

1222. Hekla. Seventh eruption.

1222-26. At sea, off Reykjanes. Four outbreaks.

1237. Seventh eruption at sea.

1240. Eighth eruption, off Reykjanes.

1245. Myrdals jökull, south-west flank, called Sólheimar

jökull.

1262. Sólheimar jökull again.

1294. Hekla. Eighth eruption.

1300. Hekla. Ninth eruption, and one of the most violent. 1311. Rauthukambar, in Austur Skaptarfells sysla.

1311 or 1332. Katla. Fourth eruption.

1332. Eruption of the Orofa jökull.

1340. Second eruption of the Orœfa; and, in same year, the tenth of Hekla; also, the only known eruption of Mósfell, in Kjósarsysla. Herthubreith also vomited; so also Trölladyngja. 1359. Fourth eruption of Trölladyngja.

1362. Eruption of the eastern portion of the Orofa; and the third of the western head.

1374. Hekla. Eleventh eruption.

1390. Hekla. Twelfth eruption.

1416. Katla. Fifth eruption.

1422. Ninth eruption in the sea, off Reykjanes,

1436. Hekla. Thirteenth eruption.

1475. Trölladyngja. Fifth eruption.

1510. Hekla. Fourteenth eruption; at the same time the second eruption of Herthubreith, and the sixth of Trölladyngja.

1554. Hekla. Fifteenth eruption, from a side crater.

1580. Sixth eruption of Katla, which then formed the huge rift between itself and Myrdals jökull. The volcano has since been called Kötlugjá.

1583. Tenth eruption in the sea off Reykjanes; and the sixteenth of Hekla.

1587. Bursting of ground near Thingvalla lake; clouds of smoke and streams of lava gushed forth.

1597. Seventeenth eruption of Hekla. 1612. Eruption of Eyjafjalla jökull.

1619. Eighteenth eruption of Hekla.

1625. Seventh eruption of Katla. In the same year, the nineteenth of Hekla.

1636. Hekla. Twentieth eruption.

1660. Kátla. Eighth eruption.

1693. Hekla. Twenty-first eruption.

1716. Eruption of ash and smoke from Ball jökull.

1717. Eyjafjalla jökull. Second eruption.

1720. Fourth eruption of the Orofa.

1721. Ninth eruption of Katla.

1724-30. Eruption of Krafla, near Myvatn.

1725. Eruption of lava in a grass-grown plain at Hítaholl, near Myvatn; followed by a similar outburst in the grass-land of Bjarnaflag. In the same year, an eruption of Leirhnukr; and also of Skeitharár jökull, west of the Orofa. That of Leirhnukr lasted till 1729.

1727. Second eruption of Skeitharár jökull, and the fifth from Oræfa jökull.

1727-28. Tenth eruption of Katla.

1728. Second eruption in the grass-land at Bjarnaflag, and, in the same year, a slight outburst from Hekla. Another eruption of lava took place in Horsadalr, near Myvatn, and filled the valley; at the same time, the earth opened near Reykjahlith and threw up ash, fire, and lava. Sithu jökull, in the south, also erupted.

1748-52. The Hverfjall was thrown up.
1753. Second eruption of Sithu jökull.

1754. Hekla. Twenty-third eruption.

1755. Eleventh eruption of Katla.

1766. Four-and-twentieth eruption of Hekla.
1772. Hekla. Twenty-fifth eruption.

1783. Eleventh eruption off Cape Reykjanes. In the same year occurred the most appalling eruption on record - that of Skapta.

1821. Third eruption of Eyjafjallajökull.

1823. Katla. Twelfth eruption.

1845-46. Hekla. Twenty-sixth eruption.
1860. Katla. Thirteenth eruption.

1861. Skapta threw up ash and sand.

1862. Trölladyngja erupted ash. There is much uncertainty about this explosion.

From the above-given list it will be seen that the number of eruptions from—

Hekla, since 1004, inclusive, have been 26.

Katla, since 894, inclusive, have been 13.
At sea, since 1210, inclusive, have been 11.
Trölladyngja, since 1150, inclusive, have been 7.
Orofa, since 1332, inclusive, have been 5.

There have been eighty-six eruptions, including outbreaks of lava, mentioned in some of the Icelandic histories, but the date of which it is impossible with accuracy to determine.

These outbursts have taken place from twenty-seven different spots. Some of these vents have been active at several different periods, whilst others have erupted but once.

The intervals between these explosions have been most irregular. Those of Hekla have varied from six to seventy-six years, and the intervals between the eruptions of Katla from six to three hundred and eleven years.

At periods of peculiar activity more volcanoes than one have vomited simultaneously, as, for instance, in the year 1840, when the Orofa, Hekla, Mósfell, Herthubreith, and Trölladyngja erupted together; or, in 1510, when Hekla, Herthubreith, and Trölladyngja poured forth fire and molten rock at the same time. From 1724-30 was the period of greatest activity, twelve eruptions having taken place in those six years. The interval of greatest length between outbreaks of subterraneous fire was between the eruptions of Trölladyngja, in 1510, and Hekla, in 1554, a period of forty-four years. Between those of Hekla and Trölladyngja, in 1436 and 1475 respectively, thirty-nine years elapsed.

Lava breaks forth not only from mountain sides, but from the grass-land under foot. The earth gapes and pours forth a flood of fire or casts up scoriæ, where meadows had previously existed. Such eruptions took place near Myvatn, in 1725, and at Thingvellir, in 1587.

Lava and obsidian.

Surturbrand.

The traveller notices many instances of the lava having thus welled up and overflowed older strata.

Beds of lava of this nature exist in the midst of the Storisandr, at Olfus, and throughout the Gullbringu sysla.

Immediately after an eruption has taken place, the volcanoes of Iceland relapse into quiescence, and no smoke or steam rises from them, as it does from Vesuvius and Etna.

The great majority have no circular craters; some have split themselves in the fury of explosion, and the lava has flowed from their sides, whilst the fire and water have found vent at the gashed crown. The perfectly symmetrical craters are Eldborg, Hverfjall, Vilíngafjall, Borg in Vithidal, and every mountain named Skál.

The lava stream from Eireks jökull we distinctly traced to the mountain roots. It had not flowed from the summit, but from a chasm at the base. The Odatha Hraun is the most extensive lava bed, covering a space of 1,160 square miles. It has flowed from Trölladyngja and Herthubreith, and its recesses are quite unknown. It extends farther north than has been represented by Gunnlaugson, and reaches indeed as far as Burfell. The second largest bed is more broken and intercepted by hills and lakes. It extends from Skjaldbreith and Hlöthufell to Reykjanes, a distance of seventy-three miles. The tract around Hekla covers an area twenty-five miles long by ten broad.

Obsidian has flowed from some of the volcanoes, as well as lava. The most important streams are near Krafla, Hekla, and at As, in Hvítárdalr. I found coarse obsidian on Ók.

As already stated, the great mountain system of Iceland is formed of Palagonite tuff. The principal places where this rock has been pierced by trachyte are Baula, Thorishöfthi in Kaldidalr, a portion of Ók, and Laugarfjall, above Geysir.

One of the most singular formations in Iceland is the surturbrand, a species of lignite, which lies in beds between clinkstone and trap. The wood is brightly glossed and black, free from all admixture of sulphur, very splintery in fracture. Logs and branches are preserved with their knots and roots; the circles denoting the age of the tree are very distinct at the ends of the fragments. In several places a layer of leaves overlies the coal in beds of four to six inches in thickness. The impression of the leaves, with all their delicate fibres, is perfect and very beautiful. The leaves belong to the poplar, willow, and birch.

The alternation of basalt and surturbrand deserves peculiar attention from geologists, as the existence of leaves, and absence of marine shells in the deposit, seems to point out that there