238 TRANSACTIONS OF THE ROYAL CANADIAN INSTITUTE _ [VOL. XI 
(Plate XXVII, fig. 36). It would appear that this fact has a bearing 
upon the grade of symmetry of the crystal. 
2. ACID CORROSION OF SPODUMENE. 
In order to obtain etch-figures upon the prismatic faces of spodu- 
mene, a small cleaved fragment was exposed to the action of concentrated 
sulphuric acid and fluorite over a low bunsen flame. After an exposure 
of five minutes no result was visible, but when the same fragment had 
been subjected to an additional exposure under the same conditions 
for ten minutes longer, numerous, clearly defined pits were observable. 
Of these primitive pits three types were noted which were bounded 
by three, four and five sides respectively. The triangular form appeared 
to be the youngest. 
These typical primitive pits were each bounded by one short, straight 
side and two larger, curved ones (Plate XXVI, fig. 10). TheangleB AC, 
which contained the deepest part of the pit, was read in one sharply 
defined example as 80° 48’. These pits were shallow and gave no indica- 
tions of figure faces, but were simply slight depressions deepening 
towards one corner. Along with them were others which, judging from 
their depth and distinctness, were somewhat more mature. In them 
the sides had increased in number to four, and were no longer curved 
but straight. Instead of being mere shallow depressions, these pits 
were enclosed by four definite figure-faces, two being unequal scalene 
triangles and two unequal deltoids (Plate XXVI, fig. 11), but even yet the 
structure was somewhat lacking in clearness. It will be noticed that 
they could be produced from the pits of the first type by truncating 
the angle B A Cby theline DE. In addition to these two forms, there 
were a few which at first appeared to belong to another group charac- 
terized by a five-sided outline (Plate X XVI, fig.12). These may, however, 
be considered as derived from the four-sided pits by a further replace- 
ment of the angle BCA by the lineG F. None were observed of a shape 
which would suggest the replacement of the angle A BC. It will be seen 
then that the three main types of pits produced upon the cleavage face 
of spodumene may be looked upon as variants of the same primitive 
type, and further, as representing thre. stages of growth through which 
the individual pit would pass if conditions were favourable. 
Along with these occurred some examples of a fourth type which 
had a more distinctive appearance, owing to the occurrence of beaks. 
This has been supposed by some investigators to have a bearing upon 
the question of the grade of symmetry shown by the crystals of this 
mineral and others, especially diopside and colemanite. They are 
