of the Buchan District 25 



minute black granules, and are therefore irregular ; (c) very 

 numerous granules and crystals of magnetite ; (d) very 

 numerous prisms and needles of apatite. 



In this ground-mass are : — 



Triclinic felspars, most of which are compounded of rather 

 wide lamellae. One crystal is, however, very compound 

 (albite law), the lamellae being very narrow. Some few 

 have no striations. The optical angles measured were — 



OP (001). 



00 P 00 (010). 



00 P 00 (100). 



3° 30' 



13° 



21° 



Enstatite very plentiful in prismatic forms of smaller 

 size than usual. Alteration has so far proceeded that but 

 little remains of even the chloritic minerals. The prisms 

 are all dull, rather opaque and cloudy, with flaws and cracks 

 lined with iron ores. 



Augite. — In less amount than usual, but otherwise similar 

 in character, and alterations to the instances described 

 already. 



Magnetite, — A few large rectangular crystals. 



The principal alteration products are enstatite to chlorite, 

 and some of the felspars to aggregates of colourless or slightly 

 yellow doubly refracting flakes, and of magnetite to ferric 

 hydrate. Flakes of viridite are also numerous in some few 

 of the felspar crystals. 



2. A coarse breccia of fragments of No. 1. 



3. Vesicular Diabase porphyrite. This is about fifteen 

 feet in thickness. A thin slice showed that it consists of a 

 ground-mass composed of — («)yellowish, slightly micro-felsitic 

 basis, (b) brown translucent to opaque spherulitic bodies 

 (these are so numerous as to make the ground-mass very 

 opaque), (c) many minute felspar prisms, (d) magnetite grains 

 or crystals, (e) a few needles of apatite, (f) a few black 

 thorn-like microliths. In this ground-mass are : — 



Plagioclase felspars. — These are so much altered that the 

 striations are barely perceptible. Augite in colourless, short, 

 stout prisms, some of which are almost wholly converted 

 into calcite. Beside the calcite alterations, I observed others 

 which I believe to be epiclote. 



Enstatite numerous, but smaller in size than the mono- 

 clinic pyroxene. It is wholly converted into some form of 

 viridite. The vesicles in this rock are filled by agate 

 amygdules, most of which are more or less bordered with the 

 minute bright green aggregate which I have before mentioned. 



d 2 



