228 50 



there is plenty of water, these particles are constantly washed away, the water 

 consequently attaining a grayish colour. Most of the hot springs at Kerlingarfjöll, 

 and some at Hengill, are of this description. On the other liand, where the small 

 particles find an opportunity of accumulating around the springs, they mix with 

 the spring water, forming a thin pulpy kind of mud. In this way the mud pools 

 and mud volcanoes at Nâmafjall, (Hlîi'tarnâmur), Hverageröi, etc. have been formed. 

 It is an obvious conclusion that the small particles are produced by the action on 

 the rocks of sulphuretted hydrogen, or of sulphuretted hydrogen and carbonic acid 

 gas combined. 



The case is quite different in springs where nitrogen is the chief constituent 

 in the composition of the spring gas. The water is then as clear as ordinary spring 

 water, and only slight sediments are to be found deposited around the springs. 



In the warm soil in the immediate vicinity of the springs a vegetation flourishes 

 which is quite luxuriant for the climate, not being checked by the poisonous sul- 

 phuretted hydrogen, as is the case in the neighbourhood of the solfataras. Where 

 the temperature of the springs is not very high, as for instance at Reykir, the 

 vegetation has advanced almost to the immediate edge of the spring, leaving only 

 a small outlet for the hot spring water. 



Practically the only thing which distinguishes these springs from ordinary 

 well springs is the bluish-gray cloud produced by the condensation of the vapours 

 arising from the hot spring water. 



The hot springs at Laugaras are similar, but owing to their intense heat and 

 the consequent violent ebullition of the water, the vegetation has retired to a greater 

 distance from the springs. 



With the exception of two geysers, the hot springs at Grafarbakki are of the 

 same nature as those in the two places already mentioned. There is a particularly 

 close resemblance between them and the hot springs at Laugaras. 



Although there are, as already shown, only infinitesimal deposits of sediment 

 at the three places mentioned, tlie spring water nevertheless contains a considerable 

 quantity of dissolved salts. 



For instance, we filled an enamelled saucepan with water from a hot spring 

 at Laugarås, and placed it in the water at the edge of the same spring. In this 

 manner the saucepan was kept hot, and after a few hours the water in it had 

 evaporated, leaving behind a considerable amount of white salts, partly crystallized. 

 All the hot springs investigated at Reykir, Laugarås and Grafarbakki were like- 

 wise proved by direct test to contain carbonates and chlorides, and most of them 

 also traces of sulphates. At all these places the water was alkaline. 



A peculiar feature of the Laugarås and the Grafarbakki "hvers," distinguishing 

 them from the hot springs at Reykir, is that the spring gas contains traces of 

 sulphuretted hydrogen. At Laugarås the sulphuretted hydrogen could only be 

 detected on the spot by means of the most delicate tests, while one of the gas 

 samples from Grafarbakki contained 0.1 "/u of sulphuretted hydrogen when it was 

 analysed in Copenhagen. That no sulphuretted hydrogen was found in the other 



