of Boston and its Vicinit?/ 



157 



SPECIES YL— BASALT. 



m 



Amorphous Basalt, Cleaveland^ p. 280. Basalt, Jameson^ vol. i. p. 369 

 Common Trap, Jiikin^ p. 236. 



External Characters. 



Its colour is greyish black. 



Its lustre is ilull^ or faintly glimmering, and glimmering from 

 the admixture of foreign particles. 



It is amorphous and coiTodetl. 



It exhales a faint argillaceous odour when breathed upon. 

 Its streak is greyish white, and dull. 

 It is hard, gives a few sparks with steel. 

 The fracture is fine grained uneven. 

 It is brittle. 



It is diflficultly frangible. 



The fragments are indeterminately angular, and not particu- 

 larly sharp edged. 



Its specifick gravity is about S.8S3. 



• Chymical Character, 

 Before the blowpipe it melts into a shining black 



Geological Situation and Locality * 

 It occurs in beds in Argillite at Charlestown, and in rounded 



masses, at Cambridge and Charlestown, 



MemarTcs, 



■+ 



This basalt contains imbedded Hornblende, sometimes scales 



of black Mica, black Feldspar, and Iron pyi 



approach to Wacke and some to Grreenstone 



SI 



s. Some vari 



The external 



