18 
pearance of a termination. The crystallized end is shown 
at the upper part of the geometrical figure on the left hand 
of the plate, and the other end on the lower part of the same 
Jigure in fibres. 
The other figure is one out of a gangue of Mica from the 
neighbourhood of Aberdeen. These crystals are net very 
regular, but are remarkable for holding small Garnets, im- 
bedded in them ;—s¢e the lower figure. 
Tourmaline is by some authors said to be distinct from 
Schorl, whilst others consider these substances only as 
varieties of each other. In some instances they appear to 
be distinct, especially when sufficiently large; but of this 
more shall be said hereafter. 
Tourmaline generally presents straight prisms *, mostly 
blackish or dark-coloured, sometimes showing a greenish 
or brownish colour at the transparent edges or flaws. My 
specimens from the Logan Rock are greenish, but those 
imbedded in Mica are brownish. Some foreign specimens 
are remarkable for varying their colour according to the di- 
rection in which they are viewed. Tourmaline is well known 
for its electrical properties. The crystals have mostly a rich 
gloss, are smoothish, with more or less numerous striz 
- placed longitudinally on the prism, and horizontally on the 
pyramids, excepting when they are approaching to fibrous, 
as below observed. 
* Sir John St. Aubin is said to have in his possession a crystal without 
a prism—a great rarity. 
P er y 
