402 COSMOS. 



year 79, from the declivities of Somma; or whether, as 

 Scacchi maintains, the newly-opened crater of Vesuvius has 

 ejected pumice simultaneously on Pompeii and on Somma? 

 What was known as pumex Pompejanus in the time of Vitru- 

 vius, under Augustus, carries us back to eruptions before the 

 time of Pliny ; and from the experience we have respecting 

 the variable nature of the formations in different ages and 

 different circumstances of volcanic activity, we should be as 

 little warranted in absolutely denying that, since its first ex- 

 istence, Vesuvius could have ejected pumice, as we should be 

 in absolutely taking it for granted that pumice — that is to 

 say, the fibrous or porous condition of a pyrogenous mineral 

 — could only be formed where obsidian or trachyte with 

 vitreous feldspar (sanidine) were present. 



Although, from the examples w^hich have been cited of the 

 length of the periods at which the revival of a slumbering 

 volcano may take place, it is evident that much uncertainty 

 must still remain, yet it is of great importance to verify 

 the geographical distribution of burning volcanoes for a de- 

 terminate period. Of the 225 open craters through which, 

 in the middle of the 19th century, the molten interior of the 

 earth maintains a volcanic communication with the atmos- 

 phere, 70, that is to say, one third, are situated on the con- 

 tinents, and 155, or two thirds, on the islands of our globe. 

 Of the 70 continental volcanoes, 53, or three fourths, belong 

 to America, 15 to Asia, 1 to Europe, and one or two to that 

 portion of the continent of Africa hitherto known to us. In 

 the South-Asiatic Islands (the Sundas and Moluccas), as 

 well as in the Aleutian and Kurile Islands, the greatest num- 

 ber of the island volcanoes are situated in a very limited 

 space. The Aleutian Isles contain, perhaps, more volcanoes 

 active in late historical times than the whole continent of 

 South America. On the whole surface of the earth, the tract 

 containing the greatest number of volcanoes is that which 

 ranges between 73° west and 127° east longitude, and be- 

 tween 47° south and 66° north latitude, in a direction from 

 southeast to northwest. 



If we suppose the great gulf of the sea known under the 

 name of the South Sea, or South Pacific Ocean, to be cos- 

 mically bounded by the parallel of Behring's Straits, and 

 that of New Zealand, which is also the parallel of South 

 Chili and North Patagonia, we shall find — and this result is 

 very remarkable — in the interior of the basin, as well as 

 around it (on its Asiatic and American continental bounda- 



