132 



VOLCANIC HOCKS OF ADEN; 



Upper 

 Gallelt. 



Wall-case 1. 



3. 



Grey vesicular lava, with the cells elongated in 

 the direction in which the stream flowed. These became after 

 wards filled with a white mineral, which has subsequently 

 in most cases, decomposed, leaving the cells empty. 



4— Reddish-brown vesicular lava, with a kw crys 

 i. «p -/— «— The vesicles have been filled with 



glassy f 



ca/c *par, which has decomposed in some cases, and the cells 

 become lined with a thin coating of chalcedony and rock 

 crystal. 



5. — Highly vesicular lava, with 



minute prismatic crystals of quartz. 



Reddish-brown vesicular lava, with a thin layer 

 of mammillated chalcedony, upon which are small lenticular 



ca/c 



spar, and 



'/ 





LAK LATA. 



Calc spar, in imperfect crystals, investing vesicu- 





8.— Grey trachyte passing into basalt, and contains 



a t n 



glassy felsp 





10. 



9.— Grey, slightly vesicular trachytic porphyry, with 



nail crystals of glassy felspar. 



PiTciiSTONE, occurring in beds 18 inches thick, be- 

 tween lava streams. 



1 1.— Pitciistone, with crystals of augite. 



12.— Greenish obsidian, with streaks and laminations 

 of other colours. A familiar example of similar appear- 

 ances may be noticed in the slags of iron furnaces, which are 

 artificial lavas, composed of silicates of alumina and lime, 

 with a little iron and other minor constituents. A.C.R. 



13. — Light-green transparent obsidian, 



glass upon lava. 



or volcanic 



14. 



15. — Pumice, with a fibrous silky structure. 



{sulphate of lime) 



16. 

 17 



Volcanic rock traversing pumice in dykes. 



)f lime. 



18. — Volcanic breccia passing into basalt. 

 19 — Volcanic breccia with much sulphur, and a thin 

 band of reddish-brown compact felspathic trap. 









i 



P 



f 



t 



# f 



•ft 



i 



ai 



jl> 



i 



by Co 



ltd 



irft; 



suns I- 



ft ■ 



t( 



11 



> 



injs mi 



C 



fie: 

 rose ei 



\ It 



orpyi 



lava. 









