194 INTERMITTENT ERUPTIVE SPRINGS. 



coals evidently suggests that they are a consequence of the action of 

 subterranean heat upon vegetable matter which happens to be con- 

 tained in the strata. And this view is strongly supported by the 

 fact, that during the explorations of the Challenger certain hot 

 springs at Furnas in the Azores were visited by Professor Moseley, 

 in which the algse became converted by the heat of the water into 

 a green, creamy, or black elastic inflammable substance. 1 And 

 just as the mud volcanoes bring to the surface fragments of various 

 rocks, so in the naphtha and similar materials we have a product 

 which might naturally be associated with such strata. Indeed, the 

 petroleum springs of the coal region of North America sufficiently 

 prove that, given the vegetable matter and even such a moderate 

 temperature as might result from the crumpling which the carboni- 

 ferous rocks have undergone, there is no difficulty in obtaining the 

 petroleum by a process of slow distillation. The special interest, 

 however, of the tiaphtha springs is twofold, and lies partly in their 

 normal existence in regions where volcanic action is nearly extinct, 

 and in the extent to which they have in former times contributed to 

 form bituminous limestones and deposits like the asphalt of the Yal 

 de Travers and many localities in Switzerland and France. 



Eruptive Hot Springs. Geysers offer another phase of volcanic 

 action in which the eruptive power remains, but instead of the 

 water being dissolved in the rock, or mechanically mixed with it, 

 only such mineral matters remain as can be dissolved in the water. 

 These phenomena mark the near extinction of volcanic energy, and 

 not only originate near to the surface, but appear to owe their 

 existence entirely to surface waters. It is remarkable that these 

 phenomena, though met with in regions so widely separated as the 

 northern island of New Zealand, the Yellowstone Valley in the 

 United States, and the south - west of Iceland, exist in areas 

 occupied by rhyolitic rocks. 



Geysers of Iceland. In Iceland they are chiefly found in the 

 Keykiadal, about thirty miles south-west of Heckla, and are situate 

 in an oblong strip of land where the marsh terminates and the 

 mountains begin to rise. The water is furnished by cold streams 

 derived from melting snows, and from the neighbouring river. The 

 geyser basins are conical siliceous domes, built up of the material 

 deposited by the waters as they cool. One of these has a height 

 of 7 feet, and is 75 feet in circumference, while the eruptive 

 throat in the centre of the basin is a circular opening 14 inches 

 in diameter. Frequently these cones stand upon coloured clays, 

 and they are so intimately connected with mud eruptions that 

 in some places mounds occur, formed entirely of clay, from which 

 water is thrown into the air to a height of a few feet. The 

 well-known Great Geyser has a well-defined cone under the hill 

 on the north-east side of Geyser Island ; but the Strokr has no cone, 



1 " On Freshwater Algse at the Boiling Springs at Furnas," &c., H. N. 

 Moseley, Jour. Linn. Soc., vol. xiv., No. 77, pp. 322, 325, 333; also W. T. 

 Thistleton Dyer, p. 326. 



