256 TRANSACTIONS OF THE ROYAL CANADIAN INSTITUTE _ [VOL. XI 
(2) The second, or immature stage is characterized by a shallow, 
rounded excavation and outlines which are composed of few and curved 
lines. 
(3) As corrosive action continues, the edges which bound the pit 
tend to become straighter and there is developed in one part a small 
but definite pit which grows larger, eventually almost filling the primi- 
tive depression, which now appears as a slight shadow. Just as the 
outlines of the primitive pit are curved, so also the earlier figure-faces 
appear to be curved, though this, as will be seen in the succeeding 
section, is due, at least in part, to the occurrence of numerous small 
faces of almost the same symbols, close to one another. During this 
process the faces become clearer and plainer, and the interpolation of 
new figure-faces of different indices and in different zones may take 
place resulting in pits of a more complex outline. 
(4) There is a point of maximum perfection, beyond which continued 
corrosion results in less distinct faces and a broadening rather than a 
deepening of the pit. 
- (5) When the edges of expanding pits overlap, leaving a fresh surface 
marked by etch hills, renewed corrosion results in the formation of a 
new crop of pits. 
4. THE NATURE OF THE FIGURE-FACES. 
The comparative regularity of the outlines of etch-figures and the 
apparent evenness of their planes, naturally suggest the idea that they 
are bounded by simple faces. This was the view of the earlier investi- 
gators, whose results were obtained by means of the microscope. Ley- 
dolt,*4 the first to consider the problem, thought it possible to express 
their relationships by means of simple symbols. 
But with the application of more exact methods, there came a grow- 
ing conviction that figure-faces are not as simple in their crystallo- 
graphic relationships as was at first believed. An examination by 
Sohncke of the four-sided pits of common salt,” showed the symbols of 
their faces to be 910 and 10, 10. Still further discrepancies were ob- 
served by F. Klocke in alum pits® whose figure-faces had the symbols 
778, (5575 150 155) 30°. 30) Cte: 
When Goldschmidt made use of his two-circle goniometer in the 
investigation of the subject, the anomalous nature of the pit faces be- 
4 Sitzb. der Akad. d. Wissensch. zu Wien, 6 Nov. 1854. 
% Jahrb. f. Min. 1875, page 941. 
% Zeitsch. f. Kryst., 2: 126. 
