264 86 



Apart from the possibility of the loss of heat occasioned by the thermal activity 

 of the springs being compensated for by heat produced by special agents or reac- 

 tions on the spot, such an extraordinary loss of heat within such a limited area 

 must apparently lead to extraordinary temperature gradients in the surroundings, 

 if the heat energy is only supplied by means of conduction. The consequent 

 gradual cooling of the surrounding strata would probably, after a short time, be 

 attended by a corresponding decline in the activity of the springs. In my opinion, 

 however, the thermal activity of the springs does not decrease as rapidly as the 

 above might lead one to expect, whence it follows that special causes must be 

 present, and the prominent cause is that the heal supplied to the hot springs is 

 chiefly by means of convection and not by conduction. 



Sulphurous springs usually come into existence immediately after volcanic 

 eruptions, and on this account it is probable that their channels extend deep down 

 into the earth; I have already adduced reasons which seem to indicate that these 

 springs are directly connected with the fluid interior of Ihe earth (magma). In 

 this case there seems to be no reason why the heat should not be transmitted by 

 convection, by means of the spring exhalations coming from the fluid magma up 

 to the surface. Through the circulation of the fluid magma, the loss of heat is 

 distributed over a wide area. 



In the secondary hot springs in the lava fields, the heat is conveyed by the 

 exhalations from the bottom of the lava up to the surface. But from the fluid 

 magma up to the bottom of the lava the heat is undoubtedly conveyed through 

 the lower spring channels. 



The nitrous hot springs apparently do not communicate directly with the 

 fluid magma, for, as I have already pointed out, it is highly probable that the 

 nitrogen and argon contained in their exhalations are of atmospheric origin. It is 

 therefore obvious that they belong to a kind of secondary hot spring similar to the 

 lava exhalations, only with this difference, that their channels go much deeper down 

 than those of the lava exhalations. In both cases atmospheric water and air are 

 caused to circulate in the channels by means of the heat energy supplied to the 

 bottom of the channels. In the case of the nitrous springs it is not very likely 

 that the heat energy is conveyed through other channels from the magma up to 

 the actual spring channels. One has more reason for assuming that the channels 

 of these springs go down so deep that the necessary heat energy is easily supplied 

 to them by conduction from the lower strata of magma. It is not altogether im- 

 possible that these springs may to some extent communicate with the magma. The 

 small quantities of sulphuretted hydrogen (and carbon dioxide) found in the spring 

 gases from Laugaras and Grafarbakki might perhaps be looked upon as the last 

 remnants of sulphurous exhalations from the interior of the earth. 



