TOPOGRAPHY AND GEOLOGY. 47 north upon the rift), lava-flood after lava-flood streamed forth in the years a.d. 1724, 1725, 1727, 1728 and 1729, spreading over the plateau in both an easterly and westerly direction. That portion of the rift, south of Asiya, runs nearly due south under the O' daSahraun, and the icy wastes of the Vatna Jokull to the coast, its course being marked by the Kverkhnhkarani and the Kverkfjoll, a range of volcanic mountains penetrating far amid the glaciers of the Jokull, possibly even as far south as the Orcefa Jokull, the volcano which marks the termination of the rift. From the Kverkfjbll, Mr. Watts saw smoke ascending during the Asiya eruption in 1875. Further, and most convincing evidence that the volcanic vents on this rift are connected with a central vent, and with each other, is found in the phenomena of the eruptions in the years 1727, 1728, and 1729. It is recorded that the Orcefa Jokull took the initiative on the 3rd August, 1727, Leirhnukr iol- lowing suit on the 21st of that month, the Jokull remaining active until the spring of the following year, when a fresh outburst at Leirhnhkr on the 18th April, and the opening of rifts and the formation of erupting craters in the Dalfjall, in Hrossadulr, and at Bjarnarflag—all three spots close together on the rift between Leirhnukr and Askja, and lying at a far lower altitude than the Orcefa Jokull—the lava-floods were diverted from the Jokull and found outlets in the four places mentioned. Leirhnukr was active during the whole of the following year. It is also worthy of notice, that in 1728, when no less than five volcanic vents were active upon a clearly traceable rift or channel, running north and south from Askja, it is recorded that ‘ this same year volcanic action was going on in the lava wastes round Hekla; ’ and the fact that ‘ volcanic action was going on in the lava wastes round Hekla,’ and not from the volcano itself, at the time that five vents upon a far distant rift or channel were erupting is, at any rate, something more than slightly corroborative of the opinion held by the author that a channel also runs in the direction of Hekla from a main central vent. From the number of lava-floods that have burst forth at various times at a distance from volcanic mountains in the same way as the one in 1875, it is evident that innumerable channels exist in the post-tertiary strata; and, to judge from the phe- nomena of the eruptions in the throe years from 1727 to 1729, and those in 1875, there is every reason to believe that these channels are connected with the great central volcanic vent beneath Asiya.

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