TRUE VOLCANOES. 359 



Barren Island, in the Bay of Bengal, a little to the east 

 of the great Andaman Island (lat. 12 15'), is correctly con- 

 sidered an active' cone of eruption, issuing out of a crater of 

 upheaval. The sea forces its way through a narrow open- 

 ing and fills an internal basin. The appearance presented 

 by this island, which was discovered by Horsburgh in 1791, 

 is exceedingly instructive for the theory of the formation of 

 volcanic structures. We see here in a complete and perma- 

 nent form what nature exhibits in only a cursory way at 

 Santorin, and at other points of the earth's surface.* The 

 eruptions in November, 1803, were, like those of Sangay, in 

 the Cordilleras of Quito, very distinctly periodical, recurring 

 at intervals of ten minutes (Leop. von Buch, in t\\v AlhandL 

 derBerl Akademie, 1818-1819, s. 62). 



The island of Narcondam, to the north of Barren Island, 

 has likewise exhibited volcanic action at a former period, as 

 has also the cone mountain of the island of Cheduba, which 

 lies more to the north, near the shore of Arracan (10 52 X ). 

 (Silliman's American Journal, vol. xxxviii., p. 385.) 



The most active volcano, judging from the frequency of 

 the lava eruptions, not only in the Indian Ocean, but in al- 

 most the whole of the south hemisphere between the merid- 

 ians of the west coast of New Holland and the east coast of 

 America, is that on the island of Bourbon, in the group of 

 the Mascareignes. The greater part of the island, particu- 

 larly the western portion and the interior, is basaltic. Ke- 

 cent veins of basalt, with little admixture of olivin, run 

 through the older rock, which abounds in olivin ; beds of 

 lignite are also inclosed in the basalt. The culminating 

 points of the Mountain Island are the Gros Morne and the 

 Trois Salazes, the height of which La Caille overestimated at 

 10,658. The volcanic action is now limited to the southern- 

 most portion, the " Grand pays brule." The summit of the 

 volcano of Bourbon, which Hubert describes as emitting, 

 nearly every year, two streams of lava, which frequently ex- 

 tend to the sea, is, according to Berth's measurement, 8000 

 feet high."f It exhibits several cones of eruption which have 

 received distinct names, and which alternately send forth 

 eruptions. The eruptions from the summit are infrequent. 



* Leop. von Buch, in the Abhandl. der Akad. dcr Wiss. ztt Berlin, 

 1818 and 1819, s. G2 ; Lyell, Princ. of Geology (1853), p. 447, where 

 a fine representation of the volcano is given. 



t Bory de St. Vincent, Voyaye av.x Qziatre Isles d'Afrique,'t. ii., p. 

 42D. 



