Krug von Nidda on tlie Mineral Springs of Iceland. 101 



constant agitation of the spring, and hence its constant boil- 

 ing temperature. Another portion is arrested in cavities, where 

 it accumulates until it is able to force a passage, and thus pro- 

 duce the eruptions. Among the numerous thermal springs 

 which I had an opportunity of examining in Iceland, the 

 Strokr is, in this respect, a solitary anomaly. No other ther- 

 mal spring, which exhibits constant agitation and boiling, pre- 

 sents at the same time the phenomena of periodical em*. '.ions. 

 Whatever could produce violent eruptions escapes in conti- 

 nued streams to the atmosphere, without ever being accumu- 

 lated for the more vigorous displays of power. 



We find it mentioned in several books of travels, that erup- 

 tions can be produced at pleasure in the Geyser and the 

 Strokr, by throwing stones or other heavy bodies into the 

 pipe. Thus Olafsen relates, that whenever he attempted to 

 sound the depth of the Geyser with the lead, water was vomit- 

 ed forth. Henderson reports, that when the Strokr was in a 

 perfect state of tranquillity, stones thrown into the funnel im- 

 mediately caused a violent subterranean noise, and that in a 

 few minutes afterwards the column of water was elevated toge- 

 ther with the stones. 



I can give no opinion as to the accuracy of these statements, 

 for the experiments which I made were not attended by any 

 result. Although I threw many stones into the pipe both of 

 the Geyser and the Strokr, not the slightest degree of activity 

 was excited in either. At the next eruption the stones were 

 again thrown out from below. I am equally unable to decide 

 on the probability of the assertion made by travellers, as well as 

 by natives, that the violence and frequency of the eruptions 

 stand in connection with rainy, stormy weather. 



The phenomena of the Geyser, the Strokr, and some of the 

 other more remarkable springs, have undergone a great variety 

 of alterations. Particular canals may be closed by the incrust- 

 ing power of the water. Caverns may fall in, and new ones 

 may be formed by the frequent shocks with which all the 

 greater eruptions are combined. But the greatest alterations 

 have always been occasioned by the earthquakes, which from 

 time to time have agitated the island. Thus, owing to the earth- 

 quake of 1789, there disappeared that spring, which, after the 



