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Show 370 GLACIER COVERED BY LAVA. and autumn of 18~8, caused the supplies of snow and ice which had been preserved in the spring of that year for the use of Catania and the adjoining parts of Sicily and the island of Malta, to fail entirely. Considerable distress was felt for the want of a commodity regarded in these countries as one of the necessaries of life rather than an article of luxury, and on the abundance of which in some large cities the salubrity of the water and the general health of the community is said in some degree to depend. The magistrates of Catania applied to Signor M. Gemmellaro, in the hope that his local knowledge of Etna might enable him to point out some crevice or natural grotto on the mountain, where drift snow was still preserved. Nor were they disappointed; for he had long suspected that a small mass of perennial ice at the foot of the highest cone was part of a larger and continuous glacier covered by a lava-current. Having procured a large body of workmen, he quarried into this ice, and proved the superposition of the lava for several hundred yards, so as completely to satisfy himself that nothing but the subsequent flowing of the lava over the ice could account for the position of the glacier. Unfortunately for the geologist, the ice was so extremely hard, and the excavation so expensive, that there is no probability of the operations being renewed. On the first of December, 18~8, I visited this spot, which is on the south-cast side of the cone, and not far above the Casa Inglese, but the fresh snow had already nearly filled up the new opening, so that it had only the appearance of the mouth of a grotto. 1 do not, however, question the accuracy of the conclusion of Signor Gemmellaro, who being well acquainted with all the appearances of drift snow in the fissures and cavities of Etna, had recognized, even before the late excavations, the peculiarity of the position of the ice in this locality. We may suppose, that, at the commencement of the eruption, a deep mass of drift snow had been covered by volcanic sand showered down upon it before the descent of the lava. A dense stratum of this fine dust mixed with scorire is well known to be an excellent non-conductor of heat, and may thus have preserved the snow from complete fusion when the burning flood poured over it. 'fhe shepherds in the higher regions of Etna are accustomed to provide ~n annual store of snow to supply their flocks with water m VOLCANIC P" RU p ,r iONS TN ICELAND. 371 the summer months b . l . spring a layer of ; I y s~mp y strewmg over the snow in the Jr o came sand a ~ . h euectually prevents th f ew me es thick which h d e sun rom · ' a once consolidated over a I . penctratmg. When lava sand feet above the level f gh aciCr at the height of ten thouthat the ice would endur 0 : e sea, we may readily conceive unless melted by volca .e ~s ong as the snows of Mont Blanc the great crater in th:l~ ~at .from below. When I visited 18~8,) I found the ere .egm~mg of winter, (December 1st h t I.c k I· ce, and in sn'WI VIces hm the inte n·o r encrusted with' ....,..e cases ot vapo between masses of ice and th urs were streaming out crater. After the disco e /~?ged and steep walls of the not be surprisinoo to find ~ertyl o Ignor Gemmellaro, it would o ' n le cones of the Icel d' I repeated alternations of lava s t reams an d glaci.e rasn. Ic vo canos, Volcanic Eruptions in Iceland w· Etna and V csuvius the m t .-1 Ith the exception of f · ' os comp ete chronol · 1 o a senes of eruptions are th f I l ogica records reaches as far back as tll . ohse o ce and : for their history h e mnt century of t e beginning of the twelfth ou~ era ; and, from that, during the whole period ~~ntur~, there Is clear evidence of more than forty and ver ' elre as never been an interval out e1· t he r an erup' tion or Y rare Y one of twenty years, W·i th- h a great earthquake s · t e energy of the volcanic action . . ·. o Intense is eruptions of Hecla have lasted s:; this reg~on, that s?me Earthquakes have often shaken th h r~a~s Without ceasmg. great changes in the interi : w oh e I~ an? at once, causing the rending of mountain~r, sue as t .e smkmg. down of hills, channels, and the appearan~e ~~e n:s;:~IO~ by nv~rs of their often been thrown u h es . New Islands have while others have J· near t edcoast, some of which still exist action of the waves. Isappeare either by subsidences or th; In th e m· terval between eru ti . afford vent to s bt P ons, mnumerable hot springs . u erranean heat and Ji! . copiOus streams of · fl ' so J.ataras d1scharooe ~ m ammable matt Th 1 ° .1erent parts of th · . 1 d er · e vo canos in dif- Phlegrrean Field, Its Ibs an. ar~ ?bserved, like those of the servm• g for a tim :s, 0 e m activity b t J! y urns, one vent often e as a SaJ.ety-vnlve to the rest · M any cones "' Hoff, vol. ii., p. 393. 2 B 2 |