240 The American Geologist. Octobor, i9oo 
The measures in distilled water resulted as follows: 
2Aqa=104^4' 104 22' 104 = 36' 
2Aqo=124 16' 124-0' 122 40' 
Whence, from the same formula: 
2 Va = 83-27' 83 38' 84' 5' 
The angles in distilled water, being larger, were more dif- 
ficult to measure exactly, and are therefore less exact than 
those in the oil. 
The following extreme variations were observed : 
2 Ha 
2 Ho 
2 Aqa 
2Aqo 
Thallium 
81=28' 
Sodium 
81-48' 
Lithium 
82=19' 
81 41' 
82=16' 
82°25' 
94 5' 
93 43' 
93°31' 
94 15' 
94°45' 
93=56' 
104 4'* 
104° 20' 
104-23' 
104=31' 
• 104=40' 
124 10 * 
123=54 
122°20' 
124=26' 123 0' 
It may be noticed that the results accepted above are not 
always the average of the extremes ; this is due to the fact that 
when a single part of the section gave a result notably different 
from those obtained from the other parts of the same crystal, 
that result was considered abnormal, and was not considered 
in finding the average, though it is given in the variations. 
If now we examine the results obtained previously we find 
that they are not numerous ; indeed it has been possible to find 
only the following: 
Chemical Composition. 
A))x. Conip. Sp.Gr. Locality 
Ab.jAn^ ;^698 Besseyre, Hte. Loire 
Ab-jAn^ 2.708 He St. Jorge. Azore.s 
Ab.,An^ 5.710 Capello, Fayal 
Ab,,An^ 2.705 Capello, Fayal 
The angle (83° 47') found in the labradorite from Carlton 
peak is therefore more than four degrees greater than any 
found by Fouque, and is 6° 31' greater than the average of his 
*Only one measure made. 
Authority 
2Va 
SiOa 
AI.O3 
CaO 
Na^O K„ 
Fouque 
7616' 
54.5 
29.8 
11.4 
4.5 .'. 
Fouque 
76=16' 
53.3 
30.1 
11.4 
5.1 .1 
Fouque 
77=0' 
53.4 
29.4 
12.5 
4.8 .5 
Fouque 
79 '^40' 
54.2 
30.3 
11.8 
3.9 .'. 
Average 
77=16' 
