Brush and Dana—Fairfield County Minerals. 37 
The crystals are invariably prismatic in habit, and show but 
one terminated extremity ; in this respect they differ from the 
ordinary childrenite of Tavistock, to which it will be shown 
they are ape related. The general be thee is shown in fig. 1. 
ec d also the optical exam- 
Hots prove that the crystals along to the ORTHORHOMBIC 
The | fundamental angles were obtained from measurements 
on a small crystal whose pyramidal planes gave excellent reflec- 
tions. The mean of a considerable number o ae whose 
extremes differed by only 11’, was taken in each c A 
goniometer provided with two telescopes was always stapled. 
These angles* are as follow. 
pap or lll a 111=46° 277 45” 
pap" or lll « 111=61° 17 54" 
From these the following axial ratio is obtained :— 
c (vert. } b a 
066299 128732 — 1-00000 
The observed planes are as follows: 
a it 100+ p 1 111 
b it 010 q a4 10988 
1 I 110 8 $2: 181 
g a-2 120 
The following is a list of the most acer angles both 
calculated and measured, so far as the last have any value. 
The angles ibtaihed from the prismatic planes in general, tee 
conspicuously the macropinacoid a (100) were in most case 
entirely unreliable. 
Measured. 
Lad 1104 110 Set AL" 76° 36’ 
Jag 120 120 = 114° 38’ 
aalI 100 £110 = «37° 60" 
Gag 100% 120 © <== BT? 14’ 
bAT O10. 716° = 67’ 10’ 52° 197 
bag G16 «120° =~: 32° 46" 
Qap mee = 69° 29’ 
Gaq 160, 932. = 62°19 
2aAs 100.1 = 65 be 
bap O10. Ill =: 66" 46” 
bag 010.233 =. 7° 13’ 
* The aon eee the normals of the planes, 
Be pple sig 
n making the sho rter lateral axis a, and giving the symbol 100 to the macro- 
oo ee follow Groth’s | Zeitschrift fir Krys- 
Miller (whose method is adopted in jook of 
Wanmeriie oieee 
true, 
