PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. 239 
1:54 grammes gave— 

Silica, . : : . 66°838 
Alumina, . ( Pale yas 
Ferrous Oxide, . 2 4 aya? 
Magnesia, . ; : 372 
Lime, : ‘ : - 942 
Potash, ’ : ; LoS 
Soda, . : : S PLORTIG 
Water, } : i - 894 
99 - 692 
5°03 per cent. of the silica insoluble ; possible impurity, quartz. 
From Hornblendic and Chloritic Rocks. 
5. At Hillswickness, on the same island of the Shetland group, strata of 
much the same general nature as those of Colafirth are to be seen; the serpen- 
tine, however, is found in but small quantities, and only of the precious variety ; 
larger beds of serpentine possibly lie in the bay to the east; all the rocks 
in the immediate vicinity are highly contorted and fractured ; large masses of 
porphyry being intruded into them in all directions, on the west side of the 
ness. 
At the spot called the “banks of Nudista” (Nithista of Greg), large quanti- 
ties of hornblende of several varieties occur, sometimes in crystals imbedded in 
snow-white albite ; and these minerals were found immediately associated with 
imbedded crystals of a pink lustrous felspar, of which the following is the 
analysis. 
Specific gravity, 2 ° 615. 
1-499 grammes yielded— 

Silica, é q ie992 
From Alumina, . . *008 
ile = 66° 711 
Alumina, . : » £9 = 813 
Ferrous Oxide, . f “9 
Magnesia, . ‘ ‘ 093 
Lime, . : , of 382 
Potash, ; 1+ 264 
Soda, . : : Bee eA) 
Water, 3 : ; *542 
99 + 934 
*7 per cent. of the silica were insoluble ; possible impurity, unknown. 
