Mr. Playfair’s Account of a 
360 
Mica and Hornblend Slate. 
1. Hornblend slate very compact. Specific gravity = 
3.0642. 
2. Micaceous schist, with hornblend and a small mixture of 
quartz. Specific gravity = 2.9385. 
3. Black micaceous schistus, fine grained containing horn- 
blend. Specific gravity = 3.0476. 
4. Micaceous schistus containing pyrites and quartz in fine 
grains. Specific gravity = 2.7293. 
5. Micaceous schistus tinged with an oxid of iron. Specific 
gravity = 2.7335. 
6. Micaceous schist with thin plates of mica and hornblend 
transverse to the stratification. Specific gravity = 2.7907. 
7. Micaceous schist with quartz in small grains. Specific 
gravity == 2.7499. 
8. Another specimen nearly the same. Specific gravity = 
2.7728. 
3. Compact micaceous schistus, grains of felspar and quartz 
intermixed. Specific gravity = 2.71845. 
10. Nearly the same with the preceding. Specific ra vity 
G= 2.7206. 
The medium specific gravity of these ten specimens is 
2.83255. 
Limestone. 
1. Granular limestone of a gray colour, containing some 
mica. Specific gravity = 2.7087. 
2. Granular limestone, silver coloured, stratified structure. 
Specific gravity = 2.8890. 
