240 PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. 
The white albite does not exhibit striation ; the pmk does, but only under 
a high power. 
Albite in small but highly-modified pellucid crystals occurs disposed on the 
surface of the larger crystals of orthoclase in the syenitic granite of the Peter- 
head district. It has specially been found in the Stirling Hill and Murdoch’s 
Cairn quarries. HaAvucutTon having published an analysis of the crystals from the 
former quarry, I have not thought it necessary to analyse those I found in 
somewhat greater abundance in the latter ; but I have (page 230) figured an 
interesting specimen from that locality, in which the albitic crystals stood m 
parallel disposition on the faces m only of the orthoclase ; and, as these faces, 
and these faces only, are pitted, and of a corroded appearance, the albite would 
seem to have been formed from the decomposition of the orthoclase, through the 
substitution of soda for potash. 

































ALBITE. 
| Cleavage Specific a: wy 7 , - ot e 
| Colour. ‘Angle. Gravity. Si. Al,0. Fe. Mg Ca, Ke, Nap. He. Total. 
Stromay, Harris,) Grey 86° 21’ 2°627 66°97 | 19°46 | ‘6 ‘21 | 2:04 | 1°23 | 9°54:| 331. 1100°36 
Colafirth, Shet- 
land—‘‘ beauti-| 
hilocks Pesce. White se 2°622 66°8 | 17°83 | 1°13 4} 1°5 |o=:92 4) Deb. “48 ||100°32| — 
Colafirth, ........ White 86 45 2°61 66°84 | 16°73 | 2°42 37 94 ‘73 |10°76 | °89 || 99°69 
Hillswick, .. ... Pink 2 2°615 66°74 | 19°81) “9 09 | 1°38 | 1°26 | 9°23 | °54 || 99°93 
.Cleavlandite,..... White wit 2°622 67°79 | 18°76 | 1°43*] ... 52 ‘76 |10°49 | ‘16 || 99°96)5 
OLIGOCLASE. 
From intrusive (?) Veins in Hornblendic Gneiss. 
1. On the north side of the little harbour of Rispond, in Sutherland, a ~ j 
great lump rather than a vein of graphic granite lies in the gneiss in a tortuous 4 
rent, cutting the strata, here nearly vertical, at right angles. 
The felspar of the granite is highly lustrous, flesh-coloured, and graphic with 
quartz throughout ; it contains sparsely diffused imbedded crystals of oligoclase, _ 
Haughtonite, and magnetite in about equal amount. 
The magnetite is of the blue-black, hackly fractured variety, which weathers 
with a brown strain, and possibly is titaniferous. The oligoclase is, as regards 
the size of the crystalline masses and its lustre, the finest in Scotland. Itis — 
pure white, in colour translucent, with striation highly developed and large in . 
character. 

* Fe,0, also ‘08 Mn. ie 
