THERMAL WATERS, GEYSERS. 749 



Central France, 1826, 1827. — On the Formation of Craters and the liquidity of lavas, 

 Quart. J. Geol. Soc, xii., 326, 1856. 



C. Lyell: Principles of Geology, 2 vols. 8vo, London. The last edition in 1872. 



L. von Buch : Physikalische Beschreibung der Canarien Inseln. Berlin, 1825. 

 (Also published in French.) — Sur les Crateres de Soulevement et les Volcans, Bull. Soc. 

 Geol. de France, ix., 355, 1838. 



C. Prevost: On Volcanoes, Bull. Soc. Geol. de France, xi., p. 188, 1810. Notes sur 

 l'lle Julia, pour servir iv l'Histoire de la Formation des Montagnes Volcaniques, Mem. 

 Soc. Geol. de France, ii., 1835. The Julia Island is the same with Graham Island (p. 

 736). All the memoirs of Prevost are remarkable for their judicious views. 



£lie de Beaumont: Recherches sur la Structure et sur I'Origine du Mont Etna, 

 Comptes Rendus, i. 429, 1835, and Mem. pour servir ii une Description Geol. de la 

 France, vol. iv. 1838. Note sur les Emanations Volcaniques et Metalliferes; Bull. Soc. 

 Geol. de France, II. iv., 1219, 1817; the distinction of acidic and basic igneous rocks 

 here first formally announced, though earlier recognized by De la Beche. 



Boussixgault: Chemical Researches on the Gases of the Volcanoes of Ecuador, 

 Ann. Ch. Phys., Hi., 5. Ascent of Chimborazo, ibid., lviii., 150, 1835. 



G. Bischof : On the Natural History of Volcanoes and Earthquakes. Edinb. New 

 Phil. Jour., xxvi., 1839, and Am. J. Sei*., xxxvi., 230, 1839. 



R. Buxsex : Ueber die Processe der vulkanischen Gesteinsbildungen Islands. Pogg. 

 Ann., Ixxxiii., 197, 1851. 



C. St. Claike Deville: On Volcanic Emanations, Comptes Rendus, 1856, 1857, 

 1862 (with Le Blanc and Fouque, on Hydrogen of Volcanoes). 



M. Fouque : On Eruptions of Etna in 1865, Comptes Rendus, 1865. 



C. Dakwix : On Volcanic Islands (from observations made during the voyage of the 

 Beagle). 8vo, London, 1811. 



J. D. Dana: Observations on the Volcanoes of some Pacific Islands, including the 

 Hawaiian Islands, and on Lrneous ejections in Australia, with general conclusions on 

 volcanic phenomena, in Geol. Report of Wilkes's United States Exploring Expedition, 

 1819. 



J. W. Judd : Contributions to the Study of Volcanoes. Geological Magazine, II., ii., 

 iii., 1875, 1876. 



4. Thermal Waters, Geysers. 



The subject of thermal waters constitutes an important part of 

 Chemical Geology, and is here only briefly treated. 



Hot springs are common (1) in volcanic regions, and occur also (2) 

 along the courses of non-volcanic eruptions ; they are occasionally met 

 with, away from all igneous eruptions, (3) on the lines of faults or 

 the axes of flexures, and sometimes (4) where there are none of these 

 conditions. The heat in the first two cases is generally of volcanic, 

 or deep subterranean, origin ; but in the others, it may come from the 

 oxydation of sulphids, or from other chemical action, in the rocks or 

 earth beneath. 



When the temperature is high the waters may be either essentially 

 pure, or strong mineral solutions. The waters often hold silica in 

 solution, whose deposition, over the region around, makes irregular 

 accumulations of a coarse opal, or rarely of quartz, and forms low 

 cones or rims about basins. Occasionally, the waters are calcareous, 

 instead of siliceous, and make calcareous basins or cones. The 

 sources of such solutions, and some of the effects resulting from 

 them, are explained on page 706, and beyond. 



