J. M. Blake on Hortonolite. 21 
From the first zone the average inclination of g! on e' is 65° 
(normals) ; Brooke and Miller give 65° 2’. From the second 
zone we have y on g', 77° to 80°; B. and M. give 79° 40 
From zone 3: g' on bz, 69° to 70°. The same authority 
give 69° 57’. The following readings were taken from another 
crystal having the planes g* better ‘defined: g', 0°s. gt aches 
h*, 268° 20'; g?, 220° 30’; g' 179°. From this the average 
for g' on g® is 40° 45’; B. and M. give 40° 27’. 
An examination of the measurements above recorded will 
show that although the mean values deduced from them ac- 
cord well with the angles of chrysolite, yet there is some varia- 
tion when the angles are taken singly, This variation is not 
genset than the imperfections of the planes gave reason to 
expec 
It is Lambebe that the planes 7, a@', and b4, occur together 
on some of the crystals. These planes lie very near together, 
and a slight rounding of the crystal might be expected to 
obliterate them. Fig. 3 represents an occasional form. It is 
introduced to show the variation in crystals upon the 
same specimen, Another small crystal had the pris- 
matic planes nearly equal in breadth, and g* largely 
developed, while the other terminal planes were 
rounded, 
Notwithstanding this great variation in develop- 
ment, the crystals. do not at all resemble those of 
hyalosiderite i in habit ; neither do they resemble cer- 
tain crystals occurring as See products, which I 
have directly compared wi em. 
The crystals 5 ape black cic bat some small portions 
are found which are transparent in thin sections, and have a 
yellowish color. A portion was selected from a section parallel 
‘separation of the optical axes. The acute bisectrix was found 
4 thai to g', and the axes to lie in a plane parallel to 
e Their separation was, from 83° to 86°, measured in olive 
“The smallness of the transparent part of the section and 
the presence of one or more oblique cracks in its interior, ren- 
‘ found the separation to be 86° to 87° about a bisectrix nor- 
to p, and in tephroite the separation of the axes for the 
