70 PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. 
The chlorite here is of a very pure appearance: it has a minutely granular 
structure composed of foliated crystals confusedly matted together. Its colour 
is bright green. It is so pervaded with crystals of magnetite that a portion suffi- 
ciently free therefrom could not be got for the determination of the specific 
gravity. 
1° gramme yielded— 
Silica, 3 : 239 
From Alumina, . ° 004 
* 243 = 24°3 
Alumina, . ‘ , . 20:°858 
Ferric Oxide, . : -  omeon 
Ferrous Oxide, : . . phos 
Manganous Oxide, . : "55 
Lime, ; é P : * 504 
Magnesia, * : ~ aan 
Waters ~ ; : » it o4ay 
From Mica Slate. 
2. The great band of this rock which passes from north-east to south-west 
through the lower Highlands of Scotland is everywhere characterised by thin 
rifts and layers of quartz, which presents features which are markedly different 
in the different districts where the rock occurs; and there are three very 
characteristic bands of quartz which follow its strike, though not without 
frequent interruptions in the continuity of their course. 
The rock itself is not possessed of well-marked features until in traversing 
westward we reach the neighbourhood of Ben Bhrackie. Here the quartz 
presents itself in nodules and lamine; these are much flawed, and they 
are characterised by having every here and there a disposition to a yellow 
coloration, which is sometimes very brilliant. The yellow appears sometimes 
only disposed in spots, in either a milk-white or in a colourless variety. It 
has much the appearance of staining ; but from the coloration appearing fre- 
quently in the interior of the stone and not on its surface, it can be no staining 
from without, even if we admitted that an outside stain could do more than 
lodge in cracks. 
After having collected specimens of this bright yellow quartz from many 
localities, I have discovered it to be due to the decomposition of crystals of 
pyrite ; these, now converted in greater part into limonite, lie in the centre of 
the coloured portions. 
