
PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. 235 
Most of those in the first column are vein felspars; of those in the second column 
only Rispond, Urquhart, and Cowhythe are vein felspars, and these are all 
graphic with quartz. I have never seen one of the corded felspars graphic with 
quartz. 

The structure which is visible to the eye, aided by the power of a lens, has, 
thus far, alone been considered ; but when thin slices of the amazonstone are 
examined in the microscope, especially with the aid of polarised light, a still 
‘more intricate and wonderfully beautiful arrangement of the parts unfolds 
itself. 
The lineation on ¢, which is parallel to its edge, but transverse to the 
corded structure, is seen to be the result of the intersections of acutely wedge- 
shaped crystals, two sets of which interlace with each other, like the teeth of 
two combs placed in opposition with forcible mutual insinuation. 
With parallel Nicols, one set of these crystals—the teeth, as it were, of one 
of the combs—is highly coloured, the other being colourless ; but each indivi- 
dual crystal—each tooth of the comb—is transversely banded by stripes of 
complimentary colour ; as if itself built up of myriad crystals,—a pile of numer- 
ous twins, the length of the individuals whereof diminishes insensibly to the 
summit. . 
With crossed Nicols all this disappears from the lately coloured set,—that 
previously colourless assuming an identical appearance. 
The twinning thus developed,—being at right angles to the twin face of the 
large crystal, and also at right angles to the supposed twin face of the myriad 
individuals which build up the corded layers,—produces therewith a structure 
of wonderful intricacy, and one which is altogether explicable. 
The appearances, when examined by polarised light, of slices cut parallel to 
¢ and to b, are shown in the plate. 
No optical phenomenon whatever is developed in slices parallel to a; this 
goes to negative the supposition of there being a twinning of crystals in the 
inclosed oligoclase. 
ALBITE. — 
From Granitic Dykes in Hornblendic Gneiss. 
1, From the vein on the south shore of Harris, facing the rocky islet of 
_Stromay. This locality is noted in an old work, the entry being “ moonstone 
from granite, opposite the Rock of Stromay.” The exact spot, which is near 
the water edge, on the terminal face of the vein, was refound by Dupggon. 
The mineral much resembles the moonstone of Norway, being possessed of a 
