Mineralogy of Sky. 95 



I have concluded, perhaps without sufficient evidence, that the 

 pitchstone both of Ben-na-Caillich and of Glamich, has been 

 detached from veins. This deduction is made from the small 

 quantity of fragments which are to be found, and from the circum- 

 stance that all the pitchstones of Scotland hitherto observed ac- 

 tually occur in veins. 



A large portion of the summit of Glamich has the power of 

 affecting the magnetic needle at even a considerable distance, a 

 property extremely common in the rocks of this family. I was 

 desirous of ascertaining if any regularity existed in the position of 

 the magnetic poles, similar to that which Humboldt has observed 

 in a rock of serpentine which he has described : for which purpose 

 I observed the affections of the needle over many parts of the 

 space as far as that was accessible, anid I have represented them In 

 the accompanying diagram, PI. 3, fig. 1. 



A consideration of those positions in the diagram will explain 

 immediately that which would require much circumlocution to 

 describe in words. In five places, extending from the eastern to 

 the south-western side of the ground Included in the circle, it will 

 be seen that the needle remains uninfluenced. At the northern 

 limit of the hill its position is equally true, but from the strength 

 of its polar tendency, I conceive It was there affected by the coin- 

 cidence of its position with the meridian of some neighbouring 

 magnet, although by some oversight I neglected to take any other 

 bearings near the same spot which might have verified this suppo- 

 «itIon. On the north east rhumb In five several places takea at; 

 the distance of five yards from each other, the positions are such aa 

 could not result from the influence of any one magnet, however 



