Temperature of Springs. 29 



that these explanations are insufficient, yet it is difficult to sub- 

 stitute a more probable one in their place. We know, says Ber- 

 zelius, that near many active volcanoes hot spnngs pour forth im- 

 mense quantities of water. We may conclude, from their tempe- 

 rature, that their channels pass near the centre of volcanic action, 

 from which they acquire their heat. Their water, besides, holds 

 in solution many ingredients which are foreign to that of or- 

 dinary springs ; for instance, the above mentioned salts of soda, 

 and a much greater quantity of silica than is found in ordinary 

 springs. The hot springs of Iceland are a well known ex- 

 ample of this. The circumstance of these waters, in some places, 

 containing sulphuretted alkah, he views, as shewing, that, on 

 the spot where the water dissolved this salt, the operation of 

 the volcano had not extended far enough, to oxidise all the 

 oxidizable substances, or had M'ithdrawn itself, before its action 

 was completed^, He now makes use of extinguished volcanoes, 

 in which the crater has been closed by congealed lava, filled 

 with ashes, sand, and rubbish, and the glowing focus has gra- 

 dually cooled. But thei'e is found, as he correctly remarks, 

 not the smallest loss of temperature by radiation, but the 

 warmth can only escape through the mass of the surrounding 

 rocks, and as these are known to be the worst conductors of 

 heat, thousands of years might be required ere they reached the 

 mean temperature of the earth. But the springs existing near 

 a volcano continue, after its extinction, to flow through their 

 former canals only so long as the water existing is supplied from 

 the atmosphere, and must issue forth to the surface as formerly, 

 warm and saliferous, as long as they meet in their course with 

 salts to dissolve, and as long as the places through which they 

 flow are heated by the proximity of the still warm focus of the 

 extinguished volcano, &c. &c. 



Against this view of Berzelius, Von Hoff * observes, that we 

 can by no means attribute such a small conducting power to 

 the materials of which the interior of the earth, or earth's crust, 

 consist, as that for thousands of years they should preserve such 

 a temperature as that must be which can produce the phenome- 

 na we observe in such springs when they come under our ob- 

 servation at the surface ; for, from the mean density of the 

 " (ieugnostical Observations on Cai-lsliatl, lli'25. j). S3. 



