120 COSMOS. 



which consequently do not simply reduce and destroy, but 

 appear in the character of creative powers, and form the 

 materials for new combinations. A considerable portion -of 

 very recent, if not of the most recent, mountain-strata, is the 

 work of volcanic action, whether effected, as in the present 

 day, by the pouring forth of molten masses at many points 

 of the earth from peculiar conical, or dome-shaped elevated 

 stages, or, as in the early years of our planet's existence, 

 by the immediate issuing forth of basaltic and trachytic rock 

 by the side of the sedimentary strata, from a net-work of open 

 fissures, without the intervention of any such structures. 



In the preceding pages I have most carefully endeavoured 

 to determine the locality of the points at which a commu- 

 nication has long continued open between the fluid interior 

 of the earth and the atmosphere. It now remains to sum 

 up the number of these points, to separate out of the rich 

 abundance of the volcanoes which have been active in very 

 remote historical periods, those which are still ignited at the 

 present day, and to consider these according to their division 

 into Continental and Insular Volcanoes. If all those which, 

 in this enumeration, I think I may venture to consider the 

 lowest limit of the number, were simultaneously in action, 

 their influence on the condition of the atmosphere, and its 

 climatic, and especially its electric relations, would certainly 

 be extremely perceptible ; but as the eruptions do not take 

 place simultaneously, but at different times, their effect is 

 diminished and is confined within very narrow and chiefly 

 mere local limits. In great eruptions there occur around the 

 crater, as a consequence of the exhalation, volcanic storms, 

 which being accompanied by lightning and torrents of rain, 

 often occasion great ravages ; but these atmospheric pheno- 

 mena have no generally extended results. For that the re- 

 markable obscurity (known by the name o ithe dry fog) 

 which for the space of several months, from May to August 

 of the year 1783, overspread a very considerable part of 

 Europe and A sia, as well as the North of Africa while the 

 sky was seen pure and untroubled at the top oi the lofty 

 mountains of Switzerland could have been occasioned by the 

 unusual activity of the Icelandic volcanicity, and the earth- 

 quakes of Calabria, as is even now sometimes maintained, 

 seems to me very improbable on account of the magnitude of 



