Royal Institution. 151 



placed the immense snow-fields which crown the summits. From 

 the arches and fissures of the glaciers, vast masses of water issue, 

 falling at times in cascades over walls of ice, and spreading for miles 

 and miles over the country before they find definite outlet. Exten- 

 sive morasses are thus formed, which lend their comfortless monotony 

 to the dismal scene already before the traveller's eye. Intercepted 

 by the cracks and fissures of the land, a portion of these waters is 

 conducted to the hot rocks underneath ; here meeting with the vol- 

 canic gases which traverse these underground regions, both travel 

 together, to issue at the first convenient opportunity either as 'an 

 eruption of steam or as a boiling spring. 



The origin of the water which feeds the springs is here hinted at. 

 That origin is atmospheric. The summits of the Jokull arrest and 

 mix the clouds, and thus cause an extraordinary deposition of snow 

 and rain. This snow and rain constitute the source from which the 

 springs are fed. The nitrogen and ammonia which occur, without 

 exception, in every spring, exactly as we find them in rain-water, 

 furnish the proof of this ; for the known deportment of these sub- 

 stances preclude them from being regarded as real volcanic products. 

 The springs of Iceland permit of being divided into two great 

 classes ; one class turns litmus paper red, the other restores the 

 colour ; one class is acid, the other alkaline. Periodical eruptions 

 are scarcely ever known to occur among the former, while to the 

 latter belong the Geisers of the island. Here then we have two 

 facts which form the termini of a certain chain of operations — the 

 water of the clouds and the water of the spring : in its passage from 

 one terminus to the other is to be sought the cause of those changes 

 which the water has undergone. 



In seeking insight here, experiment is our only safe guide. Let 

 us endeavour to combine the agencies of nature, and see whether 

 we cannot produce her results. Sulphurous acid is one of the most 

 important gases which the water encounters in its passage. Now 

 if a piece of palagonite, the rock through which the water filters, be 

 heated with an excess of aqueous sulphurous acid, it dissolves in the 

 cold to a fluid coloured yellow brown by the presence of peroxide 

 of iron. On heating the fluid this peroxide is converted into prot- 

 oxide ; a portion of its oxygen goes to the sulphurous acid, forming 

 sulphuric acid, which combines with the bases of the rock and holds 

 them in solution. This is the first stage of the fumarole process. 

 But if the process ended here, we might expect to find the dissolved 

 constituents of the rock in the resultant spring, which is by no means 

 the case, as a glance at the following table will show. 

 Relation of Bases. 



In Palagonite. In the Suffion water. 



Oxide of iron . . . . 36*75 0*00 



Alumina 25*50 12*27 



Lime 20*25 42*82 



Magnesia 11*39 29*42 



Soda 3*44 9*51 



Potash 2*67 5*98 



100*00 100*00 



We see here that the rock contains a large quantity of the oxide 



