406 M. Descloiseaux's Physical and Geological Observations 



oxidation of the alkaline sulphurets in contact with the 

 atmosphere. 



We can conceive that the water of the Geysir, passing into 

 the state of vapour at a very high temperature in subterranean 

 conduits formed by felspathic rocks, attacks their sides, and 

 is thus charged with the salts which the analysis discovers 

 in it. 



Beside the analysis of the watei- of the Geysir, the memoir 

 of M. Damour contains those of several of the springs of 

 Reykir, on the south coast of the island, and that of the water 

 of Laugarnes, situated at a short distance from Reykjavik. 

 All these waters are alkaline and siliciferous ; and, akhough 

 the proportions of the substances which they contain are 

 different in each, they offer, like that of the Geysir, a constant 

 relation between the oxygen of the silica and that of the bases: 

 only, the thermal springs of Reykir deposit, like the Geysir, 

 numerous siliceous concretions, whilst that of Laugarnes forms 

 none at all. The experiments of M. Damour explain this 

 difference very well ; for in the waters of Reykir, the con- 

 stant relation between the oxygen of the silica and that of the 

 bases is as 2 : 1 ; and after subtracting the quantity of alkalies 

 necessary to saturate the chlorine and sulphuric acid, this re- 

 lation becomes as 8 : 1. In this state of saturation, a part of 

 the silica ceases to be soluble and is deposited. 



In the water of Laugarnes, on the contrary, the primitive 

 relation of the quantities of oxygen is as 3:1, as for the 

 Geysir, and this relation, after the saturation of the chlorine 

 and the sulphuric acid, becomes as 6 : 1, numbers which re- 

 present an alkaline silicate entirely soluble in water. 



Strokkur. 



The Strokkur, the Icelandic name of which, signifying 

 churn, well indicates the continual movement of the water in 

 the channel which contains it, is situated at about sixty metres 

 to the south of the Great Geysir. It has not, like the latter, 

 formed itself a regular and conical basin ; the waters occupy 

 a sort of level well, the edges of which are only encircled 

 by a rounded mound, and worn by the frequent passage of 

 the waters. 



The dimensions of this channel are as follows : — 

 Total depth below the surface .... 15^' 55 



Diameter of the opening 2'"'40 



Diameter at 8">-30 below the surface . . 0'»-26 



The channel of this second jetting spring is therefore irre- 

 gular, and its diameter diminishes rapidly from the surface to 



