230 PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. 
An admixture of it with the orthoclase would introduce both soda and lime, 
—albite would only bring in the former, and then only at the cost of simultane- 
ously increasing the quantity of the silica,—which oligoclase would not do. 
Again, albite is exceedingly rare in Scot- 
land in granite. I only know it at Stirling Hill 
and Murdoch’s Cairn quarries near Peterhead, 
and in smaller quantity in the quarry of 
Craigton, Hill of Fare ; and at these localities 
it does not occur in veins, but in druses in the 
granitic mass. 
Riiiociee Cote Albite, moreover, it is well known, weathers 
less rapidly than orthoclase ; but the material of these laminz, or whatever 
they be termed, weathers decidedly more rapidly. 
And lastly, albite is not paragenetic in time with orthoclase—the latter is 
always proterogenetic to albite, the crystals of which are generally disposed on 
the top of the former ;—indeed in Murdoch’s Cairn the albite is evidently a pro- 
duct of a change in the orthoclase; being always disposed on apparently 
corroded m faces of the latter, with their axes accordant. (See figure.) 
Oligoclase, on the other hand, is in all respects paragenetic with orthoclase,— 
at Lairg they are imbedded side by side in quartz; at Sclatty, Rubisiaw, Craigie- 
buckler, &c., they are mutually assertive, and mutually interpenetrating. 
At the very locality in question, however, though ordinary albite does not 
occur, yet the sheafy Cleavlandite variety is somewhat rarely found ; but, 
singularly enough, it is here markedly proterogenetic to the amazonstone,— 
forming almost a “basement mineral” to the crystals of the latter. 
It has to be stated, moreover,—whether it be an argument for or against the 
above view I know not—that at certain of the localities oligoclase does not 
occur otherwise—that is in separate crystals,—indeed that is the case in those 
localities where the structure is best seen. The same thing, however, applies 
to albite, with the single exception of that at the Stromay locality. 
I have here to note that in the summer of 1876 a single mass of apparently 
a dark green felspar was broken out of a vein in Rubislaw Quarry by Professor 
Nicot and myself; this upon examination was found to exhibit the structure © 
very plainly ; but here the included and colouring material—so far as the small 
quantity obtained has as yet enabled me to determine — was the mineral 
strigovite. Some of this substance in a minute scaley form, and also im 
hexagonal crystals of the size of peas, filled small druses. 

albite. In perthite,—where there is a somewhat parallel banding of orthoclase and albite,—the two 
were probably paragenetic in time; but the microscopic structure of perthite—the only mineral in 
which there has been a chemical determination of the nature of the layers—is so different from this, as 
to form the very strongest argument against the view that the intruded material is here albite. 

