230 £. §. Dana—Herderite from Maine. 
made before these could be settled upon. The reason for this 
is that the planes, though in most cases bright, seldom afford 
sharp well-defined reflections. Their surfaces are sometimes 
irregularly striated, again uneven as if broken, and still more 
frequently they are covered by minute pyramidal prominences. ~ 
In the last case it was common to obtain two or more equally 
bright reflections, and these prominences mark the tendency of 
the crystallization to produce “vicinal” planes in the place of 
the simple plane whose position they so nearly occupy. Sim- 
ilar elevations have been observed on the surfaces of the crys 
tals of many species (see the memoirs of Scharff, Sadebeck and — 
others), and very recently Dr. Max Schuster has made a minute 
and careful study of them on the crystals of danburite from the 
Scevpi (Min. Mitth., 1883, 397), and’ has discussed their signifi- 
cance in the development of the crystalline form. It is notcom 
sidered necessary to go into the subject here, but it is evident 
that, in such cases as the above of multiple reflections, neither — 
one gives the true position of the plane in question; in gener 
it was found that the mean of the two measurements corre 
sponded to it more closely. 3 . 
The angles finally selected as the basis of calculation were 
those most nearly free from the irregularities named, the surf = 
of the planes being smooth and the reflections tolerably sharp — 
and well defined. These angles are: : 
1tr,ltoverO (011,011)  =45° 54” 
1-4-3 adj. (0114331) 9 =57" 7 
The axial ratio calculated from these angles is oe 
&@:b:e=1: 16114: 0°6823 or 0°6206: 1: 074234 
and the following list gives the most important of the calea- < 
lated angles. . oe 
