458 



Outlines of tlie Miyieralogy and Geology 



\ 



face is frequently decomposed; leaving the crystals of Hornblende 



projecting and quite perfect; in consequence of this dt'composi- 



tiou; we often find the external surface converted into a brownish 

 earthy crust. 



It is not without some hesitation, that we have pronounced 



this mineral Basalt,* between which and Wacke, there is solnti- 



mate an alliance that no two minerals oftener pass into each 



other. We h 



efully compared this 



ral with Basalt 



from 



Giant's Causeway, and 



external characters 



pi 



f- 



sent no differences, the results of their fusion are the same, and 

 this, together with its dull streak, great hardness, and diflScult 

 frangibility entitle us to call it Basalt. 



SrECIES yih^W^CKE. 



Wacke. Cleaveland, p. 287. Wacce, Jameson, vol. i. p. 376. Wacken, Kir- 

 wan, vol. I. p. 223. Wakke, ^ikin,p. 254. 



External Characters, 



Its colours are grey and purple. Of grey, it occurs blackish 

 grey and greenish grey ; of purple, lavender purple. The col- 

 ours vary much in their intensity. 



It is dull. - 



It is amorphous and cellular. 



It exhales a strong argillaceous odour when breathed upon. 

 It adheres to the tongue. 



Its streak is greyish white^ with a reddish purple tinge in 

 some parts, and is dull. 



* Sec Cleaveland's Mineralogy, pp. 283, 284. 



