not greatly diminish the danger, which consists chiefly in the fissures in the earth-filled or bridged over with ice or snow, as I have described in regard to Kötlugjá-crevices in the ice or snow-fields, and immense walls of igneous rocks, much too precipitous to scale. Add to this, the usual absence of harbours of refuge, or places of refreshment of any kind; the impossibility of procuring pasturage for horses, and the consequent necessity of making toilsome pedestrian excursions; and I question whether any mountains in the world, of equal height, are so dangerous in ascent as the jökuls of Iceland. There is thus reasonable excuse for the paucity of information on the physical geography and geology of Kötlugjá and other Icelandic volcanoes.* Kötlugjá, then, is simply a fissure on the north-east shoulder of Myrdals-jökul, the result of early subterranean disturbances. Myrdals-jökul, again, can scarcely be considered a separate mountain, but is rather part of a range which includes at least Eyafjalla and Godaland-jökuls, according to Gunnlaugsson's map, which, as I have already stated, I regard the standard map of Iceland. The height of Eyafjalla-jökul is 5432 Danish feet; the Danish foot being equal to 123th English inches, that is very nearly to an English foot. Myrdalsjökul is somewhat less lofty. Eyafjalla-jökul is a separate centre or vent of volcanic eruption. In the narrative of the earlier eruptions of Kötlugjá, given in the "Islendingur" of 16th June 1860 (No. 6), an eruption of Eyafjalla in 1821† occupies a space of not less than 3000 square miles! More modern authors estimate this unexplored territory, covered by perennial snows, at 400 square miles, and I am inclined to regard this as the more correct. * If the young undergraduates of Oxford and Cambridge-whose excessive muscular activity, youthful enthusiasm, and English love of peril and adventure annually impel them in dozens to risk limb or life on the Alps, which have been overdone and overrun by British tourists-would betake themselves instead to the jökuls of Iceland, they might manage the trip at equal, perhaps less, expense; they would reap the pleasures of novelty; they would encounter equal perils, and they might earn nobler laurels, inasmuch as they could do much to elucidate the physical geography and geology of one of the most wonderful and interesting countries in the world. † It occurred on the 19th December; was characterised by the ejection of much sand, but did little damage. The eruption is reported in the "KlausNEW SERIES.-VOL. XIII. NO. I.—JAN. 1861. с is included; but in Dr Hjaltalin's chronological account it is omitted, and we prefer to follow his example. Myrdals-jökul, according to Gunnlaugsson, is situated in 63° 40′ north latitude, and in 19° 40′ west longitude; and Kötlugjá is a little to the south of the one parallel and to the east of the other—about twenty miles inland from the south coast of the island. The range of jökuls which I have just described is frequently the first land on the coast of Iceland sighted by vessels coming from Faröe or Scotland. It has a most imposing appearance in fine weather; and, with the exception, perhaps, of Snæfell on the west coast, and Oræfa-jökul on the south coast more to the east, they are among the finest mountains to be seen on the Icelandic coast. Eyafjalla, Godaland, and Myrdals-jökuls, form a range about forty miles long, say some accounts; fifteen to twenty says Dr Hjaltalin, and twenty to twenty-four broad, running in a direction nearly E. and W. Geologically speaking, Kötlugjá consists of Palagonite-tuff, which is intersected here and there by trap-dikes of newer formation, mostly of basalt or obsidian. Though not quite peculiar to Iceland, for it occurs likewise in Sicily, yet palagonite-tuff is so largely developed in Iceland, is of such interest as the oldest geological formation therein, and is comparatively so little known to British geologists, that I need offer no apology for devoting to it a few descriptive remarks. The mineral palagonite was discovered in 1838 as the basis of the volcanic tuff of Aci Castello in Sicily, by W. Sartorius Von Waltershausen.* He was led to give it this name from having found it in a volcanic tuff very abundant in the neighbourhood of Palagonia, Sicily, during an excursion to the celebrated Val di Nota in the autumn of 1840. The similarity of this tuff to the black basalt tuff of Militello, has been turpost," a former Icelandic newspaper, not now existing. According to the Edinburgh Cabinet Library volume on Iceland, the eruption began on 20th December, and continued with intermissions till July 1823, during which latter month its chief or only ejection consisted of streams of water. When this eruption ceased, the 14th eruption (hereinafter recorded) of Kötlugjá began. Physisch-Geographische Skizze von Island mit besonderer Rücksicht auf Vulkanische Erscheinungen: abgedruckt aus der Göttinger Studien : Göttingen, 1847." A small brochure, costing in this country about 2s., and containing by far the best and most recent account of the geology and physical geography of Iceland. proved by the analyses of Dr Merklein.* Lyell describes palagonite as "rather a mineral substance than a mineral, as it is always amorphous, and has never been found crystallized. Its composition is variable; but it may be defined as a hydrosilicate of alumina, containing oxide of iron, lime, magnesia, and some alkali. It is of a brown or blackish-brown colour, and its specific density 2:43." A specimen, labelled palagonite, from the valley of Seljadalur, between Reykjavik and the Lake of Thingvalla, sent me by Professor Hannes Arnesen, lecturer on Natural History in the Government College, Reykjavik, is a substance apparently of a very composite character. To the naked eye it is of a blackish-brown colour, is amorphous and compact, and of a semi-vitreous lustre, somewhat resembling a pitchstone. It feels heavy and massive. Under the lens, it is seen to vary both in colour, texture, and density. Some portions are compact and glassy, resembling obsidian; others are spongy, porous, or slaggy, resembling pumice or slaggy-lava. Certain portions, which are generally also spongy or porous, are of a leek-green colour, and appear to be olivinic débris; others are pitchy black, and at the same time compact and vitreous, which are apparently augitic or hornblendic débris. Other portions, again, have more of a red colour, and resemble the compact Colophonite of Arendal, or the compact titaniferous Pyrope of Christiansand, both in Norway; such portions seem the débris of garnetic minerals. Lastly, there are included what appear to be fragments of jasper, hornstone, and chalcedony, or the débris thereof. What has been sent me by Professor Arnesen as palagonite-tuff from the same locality, appears to be essentially * In the "Göttinger Studien," 1845. Part I. P. 402. ↑ Manual of Elementary Geology. By Sir Charles Lyell, M.A., F.R.S. 5th edition. Lond. 1855, P. 474.; and Professor Bunsen of Heidelberg (who has recently been awarded the Copley medal of the Royal Society of London for his chemical researches) on Palagonite in the "Annalen der Chimie und Pharmacie," lxi. 268. In addition to the rocks and minerals collected by myself while in Iceland, I have been fortunate enough to receive from Professor Arnesen and Dr Hjaltalin a portion of the duplicates of the geological and mineralogical collection in the Government College of Reykjavik. Both these gentlemen are excellent geologists and mineralogists, and I therefore feel warranted in relying on the authenticity of the names and localities appended to the specimens sent me. the same thing in another form; it is more porous and friable, more intermixed with zeolites, or with small impacted fragments of obsidian-like character; more of a red tinge, or garnetic; and in some places more of a green tinge, or olivinic. These specimens are widely different from the palagonite-tuff collected by myself on the coast midway between Reykjavik and Havnafiord, or sent me by Dr Hjaltalin from the Fossvogur near Reykjavik. In the former place it is stratified and fissile, the rock forming low cliffs, which are rapidly being eroded by the waves. Some specimens were of the ordinary colour of clay, grayish, with a tendency towards a brownish rather than a bluish tint. Others were decidedly of a brown tint, while a few were ochreous from impregnation with peroxide of iron. The Fossvogur specimens are more of a brown tint, more granular and arenaceous, and evidently contain more iron than those collected by myself. The iron shows itself on weathered surfaces and in fissures, frequently as a coating of pavonine lustre or aspect. All the palagonite rocks are more or less ferruginous. Palagonite lava, from the Vatn, Reykjavik, is of so deep a brick-red colour that it resembles an iron slag, were it not for its superior lightness. To the naked eye the specimens collected by myself have the appearance of ordinary slate clays, but under the lens the following peculiarities are observable. In some specimens there are fragments of the shells of marine molluscs, beautifully preserved, but they are generally very few in number. Interspersed through the argillaceous basis are numerous masses, from the size of a pea to that of a hazel-nut, of a spongiform texture, most frequently of a leek-green colour and olivinic character, sometimes black and obsidian-like. There are also minute crystalline masses, frequently about the size of a pin's head, some white, others black, in both cases generally of a vitreous lustre, and with apparently a conchoidal fracture; and, lastly, there is occasionally much intermixed granular matter of an olivinic aspect. These contents of the tuff are, it will be at once perceived, similar to, if they are not identical with, those of the palagonite and palagonite-tuff of Seljadalur. Two series of the palagonite-tuffs collected by myself were recently kindly analysed for me by Dr Murray Thomson, Analytical Chemist, and Lecturer on Chemistry in the Royal College of Surgeons Medical School, Edinburgh. No. 1 contained silica, alumina, lime, and iron; while No. 2 contained 8.03 per cent. of iron.* The former was of a grayish colour, * Though not illustrative directly of the structure or phenomena of Kötlugjá, still, as contributions to the natural history of volcanic products in Iceland, I may here take the opportunity of recording some further analyses, kindly undertaken for me by the same chemist, of various hot-spring waters and deposits, volcanic rocks, &c., collected by myself in Iceland last summer. I have only to premise that the phrases abundant, traces, &c., used by Dr Murray Thomson in the following aualyses, are intended to give an idea of the quantity, where the amounts are not of sufficient interest or consequence to be more precisely noted. I. Water from the Hot-spring of Laugarnes, about three miles to the northeast of Reykjavik. Total solid matter in a pint, ascertained by experiment = 3.51 grs. ; sp. gr. at 60° 1000-21, water being 1000. II. Various mudst or other deposits from the same spring. No. 2. Silica, alumina, iron, manganese, magnesia, and lime. No. 3. Silica, iron, alumina ; trace of manganese, lime, and magnesia. manganese. III. Mudt-deposits from the Hot-springs of Krisuvik in the south-west of Iceland. No. 1. Iron, Lime, . large. *This large amount of silica is confirmatory of all former published analyses of the waters of the Geysers and other hot-springs in Iceland. In the various mud-deposits, Dr Thomson made careful but unsuccessful scarch after several of the rarer earths, as yttria, glucina, and oxide of cerium. |