222 PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. 
1°499 grammes gave— 

Silica,  . : : Wee y 
From Alumina, ; a OIG 
945 = 63 * 042 
Alumina, . : : oo MISE Ie 
| Lime, ‘ : : , Wit 
Magnesia, : 3 : * 213 
Potash, . c f palo 
Soda, : 5 ; oe DG 
Water, . ; . ; 0 
99-744 

Insoluble silica, -422 per cent.; possible impurity, labradorite. 
In my experience such an occurrence and association of orthoclase is unique 
in Scotland; the specimens were somewhat lighter in colour and higher in 
lustre than a specimen of the original necronite which I possess from Baltimore. 
From Pitchstone Porphyry. 
16. The “glassy felspar,” from Corriegills shore, Arran: colourless to slightly 
white translucent crystals of about a third of an inch in length, imbedded pro- 
miscuously throughout a paste of blue-black glassy pitchstone. Colourless,— 
seldom light amber-brown. These crystals were so flawed and brittle that 
neither cleavage angle nor specific gravity could be taken. 
1-°792 grammes yielded— 

Silica, . ; Ll 182 
From Alumina, . . > O86 
1498 = 66° 852 
Aluminia, ; : Sy eel 
Ferric Oxide, . : ; a} 
Lime, : ; 2 ai iets? brs: 
Magnesia, : ; ; *055 
Potash, . , p 2) 19208 
Soda, : . . . 4°316 
Water, . : : . * 864 

100 +169 
| Insoluble silica. 3° 903 per cent.; possible impurity, pitchstone. 



ee 
le Mg Bl 
