I 48. THE GEYSERS OF ICELAND. 95 



celebrated for possessing this property in an extraordinary 

 decree ; holding a large quantity of silex in solution, 

 and depositing it, when cooling, on vegetables and other 

 substances, in a manner similar to that in which travertine 

 is precipitated by the incrusting springs of which we have 

 already spoken. Iceland may be considered as a mass of 

 volcanic matter ; the only substances not of igneous origin 

 in the whole island, being deposits of surturbrand, or bitu- 

 minous wood, in which occur leaves, trunks, and branches 

 of trees, with clay and ferruginous earth. These strata 

 support alternating beds of basalt, tufa, and lava, which form 

 the summit of the hill in which the vegetable remains 

 occur. 



The Geysers, of which there are a considerable number, 

 are springs, or rather intermittent fountains, of hot water, 

 which issue from crevices in the lava. A jet of boiling 

 water, accompanied with a great evolution of vapour, first 

 appears, and is ejected to a considerable height; a volume 

 of steam succeeds, and is thrown up with prodigious force, 

 and a terrific noise like that produced by the escape of 

 vapour from the boiler of an engine. This operation con- 

 tinues sometimes for more than an hour, when an interval 

 of repose of uncertain duration succeeds, after which the 

 same phenomena are repeated. If stones are thrown into 

 the mouth of the cavity from which the fountain has issued, 

 they are ejected with violence after a short interval, and 

 ao-ain jets of boiling water, vapour, and steam, appear in 

 succession. The eruptions of the " great Geyser," wit- 

 nessed by Sir G. S. Mackenzie,* were preceded by a sound 

 like the distant discharge of heavy ordnance, and the ground 

 shook sensibly ; the sound was rapidly repeated, when the 

 water in the basin, after heaving several times, suddenly 



* Travels in Iceland, in the summer of the year 1810, by Sir George 

 Steuart Mackenzie, Bart. 



