TOPOGRAPHY AND GEOLOGY. 43 (in places three or four lava-strata will he found resting one upon the other with a stratum of tuff or conglomerate helow and another above), whereas the uppermost strata of the latter, hared by earth- quake rifts in many places to a depth of quite two hundred feet, are exclusively of lava that has been deposited unchanged, save by congelation, with thin layers of clinker-like fragments that have never been abraded by ice or waterworn, marking the divisions between ; therefore it is evident these mountain-masses, even if they were formerly a continuation of the substrata underlying the existing inland plateau, must have been upheaved prior to the deposition of the later lava-flows bared by the rifts, or the interior now covered by them must have subsided. Moreover, while .the coastal valleys and fjord inlets show signs of glacial action, the surface of the superficial sheet of lava on the plateau has never been abraded by ice, otherwise the rounded summits of the dome- shaped bubbles that are to he seen in the O'dd^iahrauri and other parts of the desert interior, would have been ground away; there- fore it is certain the later ones must have issued subsequently to the glacial epoch : that they issued subaerially and did not course down an inclined plane, hut spread out in an immense basin inclosed—or more strictly, as many gaps doubtless existed, partly inclosed—by the fragments of the older plateau is likewise certain, or they would not have been deposited so horizontally and evenly. Further proof is to he found in the facts that deep narrow fjords exist only on the east, north, and north-west coasts, where this older formation prevails, and not on the south and south-west, where the island is built up to a great extent by the igneous rock which has coursed between the masses of the older formation—the ice-clad Joklar lying inland to the south and west of the elevated plateau of the 8prengisandr and Odd^&ahraun. The way in which the fjord inlets radiate is convincing proof that they have been mostly hollowed out by glacial action ; and in the north-west peninsula the glaciers are still doing their work, though perhaps not so vigorously as of yore, the glaciers being of less extent. Save on the north coast—where we find four, whoso beds and continuous valleys lie between detached masses of this older formation—the fjords nowhere have deep continuous valleys that penetrate inland beyond the more elevated coastal region ; and the river valleys, even those of the Slcjalfandajljdt and Jokulsa, rivers which intersect the island northward from the very base of the Vatna Jokull, are of no great depth upon the plateau, hut abruptly deepen as the coast

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