HOT SPRINGS. 221 



Bishop of Pertusa, was led to adopt very correct \icws 

 regarding the phenomenon of the hot springs at Carthage. 

 On being asked what was the cause of boiling water bursting 

 from the earth, he replied, " Fire is nourished in the clouds 

 and in the interior of the earth, as Etna and other mountains 

 near Naples may teach you. The subterranean waters rise as 

 if through siphons. The cause of hot springs is this : waters 

 which are more remote from the subterranean fire are colder, 

 whilst those which rise nearer the fire are heated by it, and 

 bring with them to the surface which we inhabit an insup- 

 portable degree of heat." 



As earthquakes are often accompanied by eruptions of 

 water and vapours, we recognise in the Salses,* or small mud- 

 volcanoes, a transition from the changing phenomena presented 

 by these eruptions of vapour and thermal springs, to the 

 more powerful and awful activity of the streams of lava that 

 flow from volcanic mountains. If we consider these moun- 

 tains as springs of molten earths producing volcanic rocks, we 

 must remember that thermal waters, when impregnated with 

 carbonic acid and sulphurous gases, are continually forming 

 horizontally ranged strata of limestone, (travertine), or conical 

 elevations, as in Northern Africa (in Algeria) and in the Bafios 

 of Caxamarca on the western declivity of the Peruvian Cor- 

 dilleras. The travertine of Van Diemen's Land (near Hobart 

 Town) contains, according to Charles Darwin, remains of a 

 vegetation that no longer exists. Lava and travertine, which 

 are constantly forming before our eyes, present us with the 

 two extremes of geognostic relations. 



Salses deserve more attention than they have hitherto re- 

 ceived from geognosists. Their grandeur has been overlooked, 

 because of the two conditions to which they are subject, it is 

 only the more peaceful state in which they may continue foi 

 centuries, which has generally been described : their origin is 

 however accompanied by earthquakes, subterranean thunder, 



* [True volcanoes, as we have seen, generate sulphuretted hydrogen 

 and muriatic acid, upheave tracts of land, and emit streams of melted 

 feldspathic materials ; Salses, on the contrary, disengage little else but 

 carburetted hydrogen, together with bitumen and other products of the 

 distillation of coal, and pour forth no other torrents except of mud, or 

 argillaceous materials mixed up with water. Daubeney, op. cit., 

 p. 540.] TV. 



