79 257 



titles found in the solfataras at Hengill and Kerlingarfjöll are partly due to chem- 

 ical processes in the interior of the earth. 



The exhalations from Bjarnarflagshraun, (the lava field east of Myvatn), and 

 the northern part of Kjalhraun, (south of Hveravellir), differ from those of the other 

 hot springs in that they contain little or no radium emanation. The composition 

 of the outflowing gases coincides closely with that of the atmosphere, so that there 

 is no doubt whatever that it is atmospheric air that we have to deal with. Similar 

 exhalations of warm, damp air are fairly common in the hot lava fields of Iceland. 



In 1846 BuNSEN ' collected some gases exhaling from the crater of Hecla 

 and the surrounding lava, the latter having been produced by the eruption of 1845, 

 and having not then become cold. These gases proved to be of similar compos- 

 ition to the atmosphere. Johnstrup" collected a similar gas sample in some lava 

 in Myvatnsoræfi, east of Myvatn, which had been ejected about a year previously. 

 Christensen'' also finds that the gases emanating from a fumarole at Krisuvik have 

 the same composition as the atmosphere, and he explains the presence of air in 

 these exhalations on the hypothesis that the steam, rushing out through the spring 

 channel, sucks the air into the channel through the side walls. He considers 

 the feasibility of this much increased by the fact that lava and other volcanic 

 rocks are exceedingly porous. I think it more probable, however, that the atmos- 

 pheric air and water are in such a case in actual circulation, similar to the circu- 

 lation of water in hot water pipes. The air and the water ooze down, in cooler 

 parts, through small channels and fissures in the soil. In the heated interior of 

 the earth the air becomes hot and the water evaporates, and their density conse- 

 quently decreases. They now rise again up to the earth's surface through channels 

 which are kept hot by the current of hot air and steam. 



A most interesting point in connection with these atmospheric exhalations is 

 that they do not appear to come into contact with the real seat of thermal activity, 

 for this would at once be marked by a change in the composition of the spring 

 gases. The heat energy necessary to maintain these exhalations must be conveyed 

 to them in a special manner. The exhalations studied by Bunsen and Johnstrup, 

 from Hecla and Myvatnsoræfi respectively, provide a ready explanation of the heat 

 energy. The lava from recent eruptions had not become cold throughout, and 

 although the surface was cold, there was sufficient heat in its depths to produce 

 the circulation of air and water as above described. The same explanation is not, 

 however, applicable to the exhalations we investigated from Bjarnarflagshraun and 

 Kjalhraun. Bjarnarflagshraun was formed by the volcanic eruptions which took 

 place during the years 1724 — 1729, and is thus about 180 years old. Kjalhraun 

 is, however, older than the settlement of Iceland, 1. e. at least 1100 years old. 

 These stretches of lava would doubtless therefore have become cold throughout, if 



' Pogg. Ann. 83, 242. 1851. 



- Festskrift, p. 180; or Tidsskrift for Physik og Clieniie, 10, 232. 1889. 



» loc. cit. p. 233. 



