330 EEACTION OF THE INTERIOR OF THE EARTH 



that of the Lagoa, near Machico. The lavas have been 

 thickened by confluence, and cannot be traced far as 

 separate currents. Remains of ancient dicotyledonous 

 vegetation, and of ferns, which have been accurately 

 examined by Charles Bunbury, are found buried in 

 raised beds of volcanic tufa and mud, and sometimes 

 covered by more recent basalts. Fernando de No- 

 ranha, 3 50' S. lat., and 2 27' east of Pernambuco, a 

 group of very small islands : rocks of phonolite, con- 

 taining hornblende ; no crater, but vein-fissures, filled 

 with trachyte and basaltic amygdaloid, traversing white 

 beds of tufa. ( 473 ) Island of Ascension, its highest 

 summit 2867 feet: basaltic lavas with more glassy 

 felspar interspersed than olivine, and in well defined 

 currents which can be traced to the trachytic cone of 

 eruption. Light-coloured trachyte, often in a tufa-like 

 state of disintegration, prevails in the interior, and in 

 the south-east part of the island. The masses of scoriae, 

 which have been thrown out from the Green Mountain, 

 contain imbedded angular fragments ( 474 ) in which there 

 are syenites and granites; these fragments remind us 

 of the lavas of Jorullo. To the west of the Green 

 Mountain there is a large open crater. Volcanic bombs, 

 partially hollow, sometimes of 10 or 11 inches diameter, 

 lie scattered about in great numbers, as do also large 

 masses of obsidian. St. Helena : the whole island is vol- 

 canic ; in the interior, there are more feldspathic beds of 

 lava ; towards the sea-shore, basaltic rock, traversed by 

 countless dikes, as in the Flagstaff Hill. Between 

 Diana's Peak and Nest Lodge, in the central mountain 

 range, there is " the mere wreck of a great crater " ( 475 ), 

 full of scoriae and cellular lava. The beds of lava are 





