1916] Tur Growts or Ercu-Ficures 245 
position approximating that of diopside, while in true augites the pits 
were quite normal. This would indicate a grade of symmetry lower than 
that usually conceded to diopside. 
In a critical examination of these results Baumhauer® quoted his 
own previous investigations of Ala diopsides etched by a hot mixture 
of fluorite and sulphuric acid. In these experiments he had produced 
pits of the following four types: 
(1) Microscopical unevennesses on the unetched faces; 
(2) Long, rounded pits, frequently united to form furrows, approxi- 
mately normal to the edge between the orthopinacoid and clinopinacoid ; 
(3) Rhomboidal figures, inclined obliquely towards each edge; 
(4) Deeper, six-sided forms apparently the result of a greater de- 
velopment of (c). 
All of these would indicate the presence of a binary axis, the condition 
of monoclinic holohedrism. 
He next examined one of Pelikan’s etched crystals on which he 
found only two definite types of pits: 
(1) Deep, dark, holohedral monoclinic pits whose longest side is 
rotated slightly to the left of the edge between the clinopinacoid and the 
prism; 
(2) Rhomboidal, symmetrical, shallow pits. 
His examination of the specimen led him to believe that the other forms 
described by Pelikan were either very immature pits which if allowed 
to develop under more corrosion would become symmetrical, or were 
the result of the fusion of the two general types. In this way he dis- 
counted the conclusions of Pelikan as to the symmetry of diopside. 
The investigations of Greim which had been published nearly ten 
years earlier, did not altogether agree with those of these crystallo- 
graphers. On the clinopinacoid of his crystal from Alexander, N.C., 
etched by dilute hydrofluoric acid, he had found two types of pits, one 
bounded by four figure-faces, two parallel trapeziums and two triangles. 
The other was enclosed by five figure-faces, two pairs of parallel 
trapeziums and a rhombus. ‘The latter was parallel to the clinopinacoid 
and its sides were parallel to the upper edge of the figure and thus it 
formed the bottom of the pit. 
This very great divergence between the results of careful experi- 
menters, working with crystals of the same kind, under conditions 
practically identical, seems to be due to their comparison of pits of 
different ages. In none of these cases was anything said as to the length 
of time the corrosion had continued, and by noting the progress of the 
8 op. cit. 
