PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. 27 
loosen ; and the portions of the rock where the felspar thins off are actually the 
least compressed of the whole. This is seen by the opening out of the micaceous 
layers there, und in the immediate vicinity. 
Can it be that the metamorphism—for it is a district of considerable though 
not extreme metamorphism—has rendered the more fusible material so plastic 
that cohesion has here been tugging hard to cause it to assume actually a 
spherical form, and has been baffled only by gravitation (acting before the 
rock was tilted), which flattened out the sphere into a lens-like shape,—or 
rather retained in a lens-like shape, that which without its action would, 
through the operation of cohesion, have assumed the form of a sphere ¢ 
But the description is as yet faulty. I have used the recognised geological 
term “lenticular” as the adjective altogether most applicable—but the relative 
proportions of these masses, which vary from the size of a goose’s egg to that of a 
grampus, is a length about twice as great as their breadth. As they, however, 
thin away also somewhat as they merge into their connecting band, they present 
in section an appearance so similar to that of an eye, that it appeared to my 
fellow-workers, Dr Joass and Mr DunpGEon, that it would be most fitting that 
we should, meanwhile, designate what I have described as an occulitic structure. 
The black mica, which so clearly defines the rock layers, is here Haughtonite. 
Towards the north-east cliff of the hill it is to be found in plates of some 
inches in size; these plates protrude edgeways from the quartz veins of the 
rock, are much weather-worn, and have the colour and lustre of tarnished metal- 
lic lead. They are associated with garnet, rutile, ilmenite, and chlorite. 
The colour of their cleavage surfaces is clove-brown ; red-brown by trans- 
mitted light ; they are uniaxial, or very-slightly biaxial. 
Specific gravity (average of three specims), = 2°96. 
1°3 grammes yielded— 
Silica, ‘ ; : *453 
From Alumina, . : °0138 
“466 = 35:°846 
Alumina, . : 3 . 21°539 
Ferric Oxide, . : . | 4°467 
Ferrous Oxide, . : 2) 82306 
Manganous Oxide, — . ‘307 
Lime, 5 ; ; > e240 
Magnesia, . ; : 2, SHO76 
Potash,  . ; , aie (argo 
Soda, : : ; : "794 
Water, : , / Zee AO GG 
100-299 
Insoluble silica, 3-648 per cent. ; possible impurity, quartz. 
