520 
The Right Honourable George Knox 
8 . Basalt, from the Giants’ Causeway. 
Lost by ignition 6,051 per cent. 
Obtained by distillation 6 per cent, of bitumen and water. 
The retort contained a pumice, which broke, as in No. 1. 
9. Basalt, from Disco Island. 
By distillation, 2,312 per cent, of bitumen and water. The 
mass in the retort a pumice, which broke, as No. 1 . 
10. Obsidian. 
By ignition lost 1,75 per cent. Colour changed from ash- 
grey to reddish- white. The original specimen, in the lump, 
raven black. 
Distillation produced 0,2 per cent, of bituminous water, 
with indications of ammonia. The mass in the retort was 
a very vesicular, light, imperfectly vitrified substance, resem- 
bling the glassy pumice which adheres to, and is disseminated 
through, the Obsidian of Ascension Island. It broke as No. 1 , 
and one piece, similar to the rest, had sublimed in the neck of 
the retort. 
11. Greenstone, from Clack Hill. 
By ignition lost 2 per cent. 
Distillation produced 2 per cent, of bituminous water, 
chiefly bitumen ; part of the bitumen so volatile as to be 
evaporated by the heat of the hand, through a thick glass, in 
a few seconds. 
12. Wacke,from Disco Island. 
This mineral, which is pure wacke, is found at Inmarsoall, 
on the south coast of Disco Island, midway between the east 
