•6<H 



i 



i* 



OF ASCENSION. 



149 



4 & 5. — Cellular or vesicular basaltic lava. 



6. 



/' 



/« 



comparison with the two preceding specimens. 

 7.— Cellular basaltic lava. Some of the cells are 



yf 



sli owing 



the elongation 



8. — Vesicular basaltic lata, 

 of the vesicles in the direction of the current. 

 9. — Basalt, in one part slightly scoriaceous. 

 10. — Vesicular basaltic lava, some of the vesicles filled 



11. 



f el spa 



/< 



(si 



12. — Vesicular basaltic lava, with crystals of augite. 



13. 

 olivine. 



C 



ompact brown basaltic lava, with crystals of 



14, 14a, 14b, 14c, 14d, and 14e. — Six specimens of frag- 

 ments from the superficial part of a basaltic lava cur- 

 rent, presenting singularly twisted and convoluted forms, 

 and exhibiting lines formed by the flowing of the stream 

 while in a viscous or slightly fluid state. 



(See Darwin " On Volcanic Islands," p. 35.) 



Laminated beds alternating icith and passing into 



Obsidian. 



15. — Pearlstone, with a lamellar structure, and con- 

 taining slightly waved tortuous layers in the upper part 

 16. — Peaklstone, containing small irregular masses of 



obsidian in thin, slightly tortuous layers, with included frag- 

 ments of somewhat cellular lava, in which are small crystals 

 of glassy felspar. 



17.—- -Pitchstone, with thin parallel and slightly tortuous 

 telspathic layers, containing crystals of glassy felspar. 



17a — Small irregular nodules of obsidian, either stand- 

 ln g separately or united into thin layers, and cemented 

 °gether by soft, white and pale greenish matter, resembling 

 Pumiceous ashes. 



(See Darwin " On Volcanic Islands/' p. 57.) 



Upper 

 Gallery. 



Wall-case 2. 



