258 Natural History of Volcanos and Earthquakes. 



nations. Channels may become stopped by the incru sting prop- 

 erty of the water. During the frequent shocks Avhich accom- 

 pany the greater eruptions, some cavities may fall in, and be 

 choked up, and new ones formed. The greatest changes, how- 

 ever, are caused by the earthquakes, which from time to time 

 visit the island. Thus, during the earthquake of 1789, the 

 most important spring in the country, next to the Geyser, disap- 

 peared, and at present only steam is evolved from its mouth, 

 while the Strokr, which before this was but an inconsiderable 

 spring, increased to such an extent, that it is now considered to 

 rival the Geyser in importance. It may be observed, that the 

 eruptions of the Strokr have no connection whatever with those 

 of the Great Geyser. During the long eruption of the former, 

 the latter remained quiet, and vice versa. In general, each of 

 these numerous hot springs, which are here crowded together 

 in a very small compass, seems to be totally independent of each 

 other. This might also be inferred from the striking difference 

 in their levels. 



It seems probable from the situation of the celebrated hot 

 springs of Iceland, (of which more than fifty may be counted in 

 a space of a few acres, at the foot of a rock about 300 feet high, 

 which leans against a chain of higher rocks ;) from the numerous 

 fissures in these rocks, which are composed of alternate layers of 

 tuff"as, of slag-streams, and slag-conglomerates, as well as from 

 the fact, that the springs are confined exclusively to the lower 

 region, which extends along the foot of the hill, whilst on its 

 sides and summit are found only gaseous exhalations (aqueous 

 vapor and sulphureted hydrogen gas ;) that these springs are 

 supplied from the meteoric waters of the neighboring hillSj and 

 that, being originally cold, they are indebted for their high tem- 

 perature solely to the hot vapors which they receive from below. 

 The hot springs in Icela7id seem, therefore, to be produced in the 

 manner described at page 253. 



Lastly, If the permanent obstruction of the lava and the water 

 channels has taken place, of course no hot springs can exist, or 

 ■at least they can only flow during the cooling of the lava last 

 ejected and solidified. This seems to have been the case in the 

 volcanic district of the Siebengebirge, the Laacher See, and the 

 JEifei, as in these places no hot springs, with the exception of 

 the baths of Bertrich, are to be met with ; although in the two 



