Ixii REPORT — 1864. 



between the volcano and tlie hot spring is recognizable in the great abundance 

 of hot springs in regions where volcanic eruptions stiU occur from time to 

 time. It is also in the same districts that the waters occasionally attain the 

 boiliug-temperature, while some of the associated stufas emit steam consider- 

 ably above the boiling-point. 13ut in proportion as we recede from the great 

 centres of igneous activity, we find the thermal waters decreasing in fre- 

 quency and in their average heat, while at the same time they are most con- 

 spicuous in those territories where, as in Central France or the Eifcl in 

 Germany, there are cones and craters stiU so perfect in their form, and 

 streams of lava bearing such a relation to the depth and shape of the existing 

 valleys, as to indicate that the internal fires have become dormant in com- 

 paratively recent times. If there be exceptions to this rule, it is where 

 hot springs are met with in parts of the Alps and Pyrenees which have been 

 violently convulsed by modern earthquakes. 



To pursue still further our comparison between the hot spring and the 

 volcano, we may regard the water of the spring as representing those vast 

 clouds of aqueous vapour which are copiously evolved for days, sometimes for 

 weeks, in succession from craters during an eruption. But we shall perhaps 

 be asked whether, when we contrast the work done by the two agents in 

 question, there is not a marked failure of analogy in one respect — namely a 

 want, in the case of the hot spring, of power to raise from great depths in the 

 earth voluminous masses of solid matter corresponding to the heaps of scoritE 

 and streams of lava which the volcano pours out on the surface. To one who 

 urges such an objection it may be said that the quantity of solid as well 

 as gaseous matter transferred by springs from the interior of the earth to its 

 surface is far more considerable than is commonly imagined. The thermal 

 waters of Bath are far from being conspicuous among European hot springs 

 for the quantity of mineral matter contained in them in proportion to the 

 water which acts as a solvent ; yet Professor Eamsay has calculated that if 

 the sulphates of lime and of soda, and the chlorides of sodium and magnesium, 

 and the other mineral ingredients which they contain, were solidified, they 

 would form in one year a square column 9 feet in diameter, and no less than 

 140 feet in height. All this matter is now quietly conveyed by a stream of 

 limpid water, in an invisible form, to the Avon, and by the Avon to the sea ; 

 but if, instead of being thus removed, it were deposited around the orifice of 

 eruption, like the siliceous layers which encrust the circidar basin of an 

 Icelandic geyser, we should soon see a considerable cone biiilt up, with a crater 

 in the middle ; and if the action of the spring were intermittent, so that ten 

 or twenty years should elapse between the periods when solid matter was 

 emitted, or (say) an interval of three centuries, as in the case of Vesuvius 

 between 1306 and 1631, the discharge would be on so grand a scale as to 

 afford no mean object of comparison with the intermittent outpourings of a 

 volcano. 



Dr. Daubeny, after devoting a month to the analysis of the Bath waters 

 in 1833, ascertained that the daily evolution of nitrogen gas amounted to no 

 less than 250 cubic feet in volume. This gas, he remarks, is not only cha- 

 racteristic of hot springs, but is largely disengaged from volcanic craters 

 during eruptions. In both cases he suggests that the nitrogen may be 

 derived from atmospheric air, which is always dissolved in rain-water, and 

 which, when this water penetrates the earth's crust, must be carried down 

 to great depths, so as to reach the heated interior. When there, it may 

 be subjected to deoxidating processes, so that the nitrogen, being left in a 

 free state, may be driven upwards by the expansive force of heat and steam, or 



