Mr Poulett Scrope's Considerations on Volcanos. 351 



inferior lava. The latter mode will be often accompanied by the heaving 

 up of more or less extensive masses of the neighbouring strata. Examples 

 are given of volcanic islands, which appear to owe their elevation from the 

 depths of the sea to these different processes. Iceland, Teneriffe, Sicily, 

 and some of the Leeward Isles, are quoted as islands which have risen by 

 the joint effect of both the above modes of subterranean activity ; the 

 Isle of France, Pulo Nias, some of the Madeiras, and of the Hebrides, as 

 instances of the latter mode acting alone. The author supposes the coral- 

 line islands of the Pacific to be mostly based upon volcanic submarine 

 eminences ; their circular or elliptical figure corresponding to the ridge of 

 the central crater of a volcano. Many have been subsequently raised far 

 above the level of the ocean ; and the earthquakes, to which they are so 

 often liable, prove their elevation to be owing to subterranean intume- 

 sence, and to be still in progress, while the continual growth of fresh 

 coral on their shores, augments at the same time their horizontal extent. 



Chapter IX treats of Volcanic Systems. 



The volcanic vents observable on the surface of the globe, are arranged 

 either in detached groups, as those of Iceland, the Azores, Canaries, Cape 

 Verd Isles, &c. ; or, and this is the prevailing case, in linear trains, at a 

 greater or less distance ; often so close, that the products of the neighbour- 

 ing volcanoe are in contact, and produce strings of volcanic mountains, 

 such as occur in France, Germany, the Leeward Isles, Java, Sumatra, Ja- 

 pan, Kamschatka, &c. The most remarkable series of vents of this kind on 

 the globe, is that prodigious train which, beginning in the Andaman and 

 Nicobar Isles, runs'through Sumatra, Java, Sumbawa, Sumba, Timor, and 

 the whole group of the Moluccas, whence, taking a northerly direction, it 

 has produced the Philippines and Loochoo Isles, Japan, Jesso, the Kurile 

 group, and the peninsula of Kamschatka. Thence it diverges to the east 

 forming the chain of the Aleutian Isles, and appears to be continued south- 

 erly along the western coastof North America into California, Mexico, Gua- 

 timala, Nicaragua, Panama, and the vast volcanic range of the South 

 American Cordilleras, even to Terra del Fuego. If, as appears most pro- 

 bable, such trains of volcanic vents indicate fissures, broken through the 

 superficial strata by subterranean expansion, what a prodigious compound 

 fracture in the crust of our globe does this immense chain of volcanos 

 disclose to us. In these systems, some few vents remain occasionally ac- 

 tive, others closed, the former acting as safety-valves to the neighbouring 

 districts. In case of their permanent obstruction, some fresh vents must 

 be produced, or some former orifice re-opened ; while violent earthquakes, 

 and elevations of the neighbouring strata, will precede, or accompany 

 this change. The author then dwells on the appearances in the con- 

 stitution of the known surface of the earth, which indicate numerous 

 and forcible elevations of strata, by subterranean expansions, more 

 particularly in the elevated or mountainous districts, which, according to 

 him, are those points or lines that have suffered the maximum of eleva- 

 tion, from the extreme developement of the expansive process beneath 

 them. But since, as has been stated above, and as is shown to be con- 



