MINERALOGY OF BLACK LAKE AREA. 
39 
minutes, with the accepted values (for p 0 — 0 • 5390, q 0 =0 • 5670 or a : b : c 
— 1 * 0934 : 1 : 0 • 5894 ; = 74° 90 and it has not been thought necessary 
to tabulate those for commonly occurring forms ; those for the new forms 
are as follows: 
Letter 
Symbol 
Calculated values 
Measured angles, 
mean 
X\ 
610 . 
U = 80° 17' 
= 80° 25' 
\p = 90 00 
= 89 55 
D* 
13-0*4 
fa = 90 00 
= 90 00 
V = 64 35 
= 64 38 
Ji 
902 
to = 90 00 
= 90 00 
\p = 70 23 
= 70 20 
Ii 
701 
to = 90 00 
= 89 20 
\P = 76 07 
= 76 15 
Y 
423, . .. 
(<p = -49 37 
= -49 38 
\P = 31 18 
= 31 17 
r. 
15-4-10 
to = “67 01 
= -66 52 
\p = 31 09 
= 31 18 
s. 
534.... 
to = -43 18 
= -43 38 
\P = 31 17 
= 31 20 
Xt 
773 
to = “36 39* 
= -36 59 
\P = 58 46 
= 59 15 
di 
8* 11*4 
to = -27 18 
= -27 44 
\P = 60 20 
= 60 37 
N, 
191 
{<p = - 2 59 
= - 3 10* 
\P = 78 55* 
= 79 05 
Oi 
16*13*3 . 
to = “31 48 
= -31 29 
\P = 70 55 
= 71 06 
The following particulars are added as indicating the manner in 
which these new forms were present on the crystals : 
Y X (610) Observed three times, on two crystals, one of which was a twin 
in each case, £he prism zone was heavily striated vertically, but 
the faces (610) were fairly well defined. 
Di .(13-0*4) This form was observed independently by both writers on two 
crystals, as small, but fairly bright faces. 
Jx (902) Occurs on one exceptionally fine crystal as a very brilliant face 
of appreciable size (see Figure 7). 
Ix (701) Observed on one of the crystals of flat habit. 
Y (423) This form was observed independently on three crystals, one of 
Which is shown in Figures 7 and 8; the faces are small, but suffi- 
ciently bright to admit of accurate measurement. 
(15*4:10) These forms were present on several crystals, and are shown in 
. . . (534) Figure 6. The faces are in each case very minute, and did not 
yield very bright signals, but as will be seen from the table 
above, the mean measured angles agree closely with the values 
calculated for forms having these indices. 
