§ 1. Genesis and Geology.
“Iceland owns its existence wholly to submarine volcanic agency”—such is the statement generally made by travellers and accepted by readers. The genesis of this “Realm of Frost and Fire;” this “fragment of earth white with snow, black with lava, and yellow with brimstone;” this “strange trachytic island, resting on an ocean of fire in the lone North Sea,” where the “primary powers of nature are ever at war with one another,” is compared with the efforts, vastly magnified, which in 1811 threw up from the waters Azorean Sabrina to a height of 480 feet above sea-level. And many have assumed as its exemplar the three-coned Nyöe (Nýey) that rose during the Skaptár eruption (1783), some thirty miles south-west of Reykjanes, and sank into a subaqueous reef before the end of the same year.[52]
This is true, but not the whole truth. The basis of Iceland was recognised by Baron Sartorius Von Waltershausen to be the Palagonite[53] which forms the foundation of volcanic tufas on Etna, the Azores, Tenerife, the Cape Verds, and other Plutonic regions. It is known to the people as “Mó-berg,” the saxum terrestre-arenosum of Eggert Olafsson, translated by the dictionaries Clay-soil, but generally used in contradistinction to Stuðlaberg,[54] hard stone, the basalts, basaltites, dolerites, and others of their kind. By the older travellers, as Henderson, it is termed sandstone, and conglomérat-basaltique, while not a few have confounded it with trachyte. In Iceland this mineral substance, rather than mineral, is a far more important feature than even in Sicily.
By virtue of its composite character and different colour, this hydrosilicate of alumina is a Proteus; massive and amorphous; crystalline, muddy, sandy, and ashy; friable, porous, and spongy like lava and pumice; granular, silicious, and arenaceous; heavy and compact like slatey clays; vitreous and semi-vitreous with the lustre of pitch-stone. It is as various in tint as in texture; usually ferruginous brown, dark brown or dun yellow; grey and slate-coloured; dark with hornblendic particles; pure white where it is converted into gypsum, clay marl, and limonite with the aspect of chalk, by exposure to the action of sulphurous acid; green tinged with olivine; garnetic-red; ochreous, the effect of iron; and at times showing a ferreous coat of pavonine lustre. Palagonite lava is often “of so deep a brick-red colour that it resembles an iron slag, were it not for its superior lightness.”
Here, this Palagonite degrades to the yellow sand which contrasts so remarkably with the black Plutonian shore; there, in the lowlands it shows fissile strata horizontal like sandstone, and at times marly couches. It paves the soles of valleys and the floors of rivers; and it rises on the surface of the loftiest Heiðar (highland heaths), where earth is worn down to the very bone by rains, snows, and winds. Now it towers in huge cliffs and scaurs, irregular masses of rock overlying or underlying the traps; then it bulges into high belts of country, sierras and detached mountains, like Herðubreið and others which will afterwards be mentioned. Consolidated and in places crystallised by heat and high pressure, this produce of submarine volcanoes was elevated by the long continued action of quietly working forces, but it still displays its subaqueous origin. Firstly, it is a hydrate containing 17 to 25 per cent. of water; secondly, it is stratified as if formed of hardened ashes and modified lavas; and, thirdly, it contains broken mollusks[55] of marine types still existing, and the silicious skeletons of infusoria: a negative proof is that we never meet with it among volcanic tuffs subaërially deposited. In places it becomes an acute-angled breccia, enclosing basalts and lavas varying from the size of a pin’s head to that of a man, or rounded conglomerates suggesting that the foreign matter was deposited in a shallow sea. The fresh appearance of the shells and the presence of infusoria also tend to prove that it was deposited in a heated, at least not in a gelid sea.
Professor Tyndall finds in Palagonite the first stage of the fumarole: “If a piece be heated with an excess of aqueous sulphuric acid, it dissolves in the cold to a fluid, coloured yellow-brown by the presence of peroxide of iron. On heating the fluid, the peroxide is converted into protoxide; a portion of its oxygen goes to the sulphurous acid, forming sulphuric acid, which combines with the basis of the rock and holds them in solution.” But the resultant springs show no trace of oxide of iron which has been dissolved and has disappeared. “The very rock from which it was originally extracted, possesses the power of re-precipitating it, when by further contact with the rock, the solution which contains it has its excess of acid absorbed, and has thus become neutral. In this way, the aqueous sulphurous acid acts as carrier to the iron, taking up its burden here, and laying it down there; and this process of transference can be clearly traced to the rocks themselves.”
Upon this Palagonite floor, the “Protogæa,” or oldest formation, were laid immense tracts of sand and stratified ejections of “trap.” According to Macculloch, “the word is a cloak for ignorance which saves the trouble of investigation.” But it is still a general term for the older, lighter, less earthly and basic, and more crystalline forms than the basalts, containing intercalated pumice-tuffs deficient in shells, whilst the cavities abound in zeolites and amygdaloids.[56] Concerning the strike and dip of the trap-strata, which rise sheer from the sea, in grades and layers, steep, angular, and bare, and which outline the mural copings and stepped cones of the old coast and the jaws of the river-gorges, there are many conflicting opinions. Some hold that the strata all incline gradually and quaquaversally, more or less, towards the centre of the island; whilst others find that as a rule, they are horizontal. The expedition led by Prince Napoleon (1857) recognised convergence, and often a slope of 15° towards the grand foci of eruption that form the respective systems; for instance, the inclinaison rayonnante towards Snæfellsjökull. The author could lay down no rule, except that the steps, viewed in profile, especially from the gashes and torrent-beds, appear to recede rather than to project, to dip inland rather than seawards. The strata vary in number to a maximum of fifty; they are perpendicular courses separated by débris, and sometimes footed by déblai and humus, disposed at the natural angle—this regularity again suggests submarine deposition, and everywhere attracts the stranger’s eye.
Professor Bunsen divides the rocks of Iceland, and probably those of most other volcanic systems, into two great groups: (1.) Normal Pyroxenic, the basalts and dolerites, whence silica is almost absent; and (2.) Normal Trachytic, abounding in that mineral. The basalts[57] are of two kinds, the true, rich in, and the basaltite, which notably wants, olivine. Both are either honey-combed with drusic cavities, or perfectly compact and fine-grained; the water-rolled pieces are soft, and smooth as marble. The basalts pass by almost imperceptible degrees into dolerites (green-stones) coloured by admixture of chlorite, and often containing iron pyrites. Of less importance as a geological feature, are the masses, veins, and crests of trachyte which pierce the Palagonites, the traps, and the basalts. The rock which is compared with the chain of the Puys (Auvergne), occurs, however, in an altered form at many places unsuspected by old travellers, and every explorer adds to its importance. From Reykjavik appear two gold-yellow and white-streaked peaks, associated with jasper and other forms of quartz. The Snæfellsjökull peninsula is also for the most part trachytic. The celebrated Baula (the cow), a cone rising 3000 feet high, contrasts the mechanic neatness of its whitey-grey pillars[58] with its red neighbour, Little Baula, and with the surrounding chaos of darkness; and heat-altered trachytes are found about Hekla and the Geysir. The green trachyte of Viðey, apparently tinted by chlorite, was found to contain silica, alumina, iron, and traces of magnesia. Daubeny, and a host of writers, assumed that a trachytic band, disposed upon a rectilinear fissure 200 kilometres long, bisects the island from south-west (Reykjanes) to north-east (Langanes), and represents the original Iceland, as the Longmynd and Stiper Stones are the nucleus of England. Moreover, the great centres of eruption, igneous and aqueous, were disposed upon this diagonal, flanked by the earlier Plutonic masses. Lastly, the modern volcanic chimneys were all theoretically opened in the old and new trachytic domes. M. Robert (1835) especially sought and failed to find the “trachytic band,” and, since Von Waltershausen’s visit, it has been determined that the material is the Palagonite floor traversed by the Geysir and by most of the active volcanoes.
The peculiar contrasts of the island are thus noticed by an old writer: “The king of Denmark is still master of Iceland, which is supposed to be the Ultima Thule of the ancients. The surface, though it is covered with snow, nevertheless contains burning mountains, whence issue fire and flames, to which the Iceland poets compare the breasts of their mistresses. It has also smoking lakes, which turn everything thrown into them to stone, and many other wonders which render this island famous.” Iceland, like Tenerife, owes its present general contour to subaërial volcanic action of the post-Tertiary period, the secular growth of the detached regions overlying the pockets and foci of eruption, as explained by Von Buch, together with the gradual accretion, the gift of exit-chimneys and dejections from the Plutonic cauldrons. The normal pyroxenic was followed by the felspathic formations, trachytic, acid and pumiceous, which, though comparatively modern, still date from immense antiquity. The distribution into fire-vents (true volcanoes) and sand-vents (pseudo-volcanoes), will be noticed in a future page.
The lava is composed of trachytic (silicious) and doleritic (basic) ejections, varying in weight;[59] the stone averages about half the specific gravity of granite, and in a molten state it flows at the rate of 50 to 100 yards per diem. When first cooled, the ejections are lamp-black; they are then tarnished by oxygen to brown; they become grey with lichens; and finally, the lapse of ages converts them into humus. To the latter process, Brydone, on Etna, assigned 14,000 years, and greatly scandalised our grandsires, who held sound opinions upon the date (B.C. 4004) empirically assigned to creation. We can hardly forget poor Cowper’s poor verse, and poorer sense: