152 



TRACHYTES AND LAYAS 



"Upper 

 , Gallery. 



"Wall-case 2. 



33— Pale greenish-grey, decomposing trachytic p or 



/< 



microscopical 



specks, and brown stains (decomposed crystals of augite) 

 (See Darwin « On Volcanic Islands," pp. 42 and 4S \ 



34 & 3o. 



Slightly laminated pale grey trachyte. 



36. — Pale grey laminated trachyte. 



The specimen 



thered surface — From tire base of Garden Hill. 



37. 



/' 



Pale greenish-grey trachyte, containing crystals of 



The 



«>rfww, probably derived from the sea-water with which it 



has been saturated. 



38. 



Pale greenish-grey trachyte, with numerous crys- 



felsp 



microscopical 



ssyfelspa 



41. 



specks. 

 39. 



and a few decomposed crystals of augite. 



The specimen shows a weathered surface. 



40.— Pale grey trachytic rock, honeycombed with irre- 

 gular cavities, presenting a carious appearance, and a strong 

 resemblance to silicified wood. 



Another specimen, having some of the cavities filled 

 with a white powder. 



42.— Greenish trachyte, with embedded fragments of 



obsidian. 



. 43.— Bluish-grey trachyte, with pale brown markings. 

 (See Darwin " On Volcanic Islands," p. 55.) 

 44.— Pale purplish earthy trachyte, with crystals of 



glassy felspar, and presenting a weathered surface, which 



is scoriaceous in places. 



45. — Grey trachyte, with a contorted lamellar struc- 

 ture, minute black specks, and crystals of glassy felspar. 



46. — Another variety : light grey trachyte, with crys- 

 tals of glassy felspar and angular scoriaceous fragments, 

 and streaked with numerous slightly tortuous white lines 

 which frequently expand into small cavities. These con- 



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