74 PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. 
bright-green colour. It was examined to see if the difference of the matrix 
affected the composition of the mineral to any marked extent. Its specific 
gravity also is 2° 852. 
1° 396 grammes yielded— 
Silica, . ; , : 24 * 66 
Alumina, : , ‘ 23°19 
Ferrie Oxide, . ’ * 636 
Ferrous Oxide, ; 20° 579 
Manganous Oxide, . : *29 
Lime, . ; . : “4 
Magnesia, . : : 17°79 
Water, . ; : : 12°119 
99 - 664 
5°56 per cent. of the silica were insoluble. 
The same quarry contains bands of a dark, dense, granular rock rather than 
mineral ; this is perhaps entitled to the name of potstone. 
6. A bed of limestone is seen on the highway about a mile east of Loch 
Laggan in Inverness-shire. This contains much very fine granular chlorite, of 
a grass-green colour. It is here very soft, and has a specific gravity of 2° 834. 
It contains, imbedded in its mass, large plates of brown Biotite. 
1°586 grammes gave— 
Silica, . : : 5 26> 25 
Alumina, ; : : 19-22 
Ferric Oxide, : c on 
Ferrous Oxide, ; 4 16°44 
Manganous Oxide, . ‘ 1: 02 
Magnesia, . : : 24° 35 
Water, . 4 : . IA) S0/ 
100° 62 
Insoluble silica, 2 per cent.; possible impurity, Biotite. 
From Chlorite Slate. 
7. The stone of which the houses of Portsoy in Banffshire are built is 
obtained from a quarry of a very calcareous clay slate, situated on the sea-shore 
a little to the west of the town. Immediately to the east of this, the first rock 
seen is a chlorite-slate, or rock ; this occurs as a high-tilted bed, dipping south- 
east. It contains fragmentary and angular masses of dense hornblende rock, 
