





218 PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. 
From Syenite. 
10. At ,the locality —about half a mile south of Froster Hill, near Old 
Meldrum,—whence this orthoclase was taken, the rock is as true and as simple 
a syenite as any I have seen. 
It consists sometimes solely of a pure, opaque, almost lustreless onuneleees 
acting as a paste to imbedded crystals of hornblende, of about half an inch in 
size, and of a deep-green colour. Occasionally a lighter green somewhat fibrous 
hornblende is added, very rarely a plate of a bronzy mica (? Biotite), a few 
brilliant minute brown sphenes, and small flat plates of blue-black titanic iron. 
Being in plates, they are probably not magnetite. There is no visible quartz. 
The bit of orthoclase analysed was of unusual size. It was quite crystalline, in 
broad cleavages, with a somewhat fatty lustre; it was thought to be oligoclase. 
Cream-coloured, tough, cleavage angle 89° 58’; specific gravity, 2°548. 
1°499 grammes gave— 
Silica, ; : : - 939 
From Alumina . : * 020 


Alumina, . 4 : Pe aSEM66 
Ferric Oxide, F : : * 846 
Lime, : ; 4 : 1: 046 
Potash, ; ; : ED pees 
Soda, P é : : 2-060 
Water, ; ; : 3 - 808 
99 - 506 
Insoluble silica, ‘(027 per cent.; possible impurity, hornblende. 
From Micaceous Gneiss. 
11. The specimens I have analysed from the above rock were taken from 
what are regarded by me as being the largely amplified felspathic layers of 
the gneiss; they are so regarded because I have observed a gradual augmenta- 
tion of these layers, from quite a thin and crypto-crystalline band lodged 
between the dark mica layers, to bands, or what might even be called beds of 
several feet in thickness ;—their thickness, however, is ever varying ; they never 
cut the micaceous layers, and the contortions and foldings of the rock are 
common to both. 
They are to be regarded, I believe, as the results—the incipient results—of 
an exalted metamorphism ;—a metamorphism which has accomplished the 
segregation, and probably the fusion of the felspathic material; but fallen short 
of affecting the more intractible mica. 
When the fluent felspar, sapping into the darker layers, loosens the conti 
