ELASTIC CONSTANTS otf ROCKS. 51 
therock is absolutely fresh. The structure is allotriomorphic, and there is a 
tendency to a parallel arrangement among the grains of the darker con- 
stituents. 
A photomicrograph of a thin section of the rock taken between crossed 
nicols in polarized light and magnified 30 diameters is shown in Plate XII B. 
The elastic constants were determined on a square prism of the rock, and 
as the rock is very strong, the loading was carried up to 15,000 pounds 
instead of 9,000 pounds, as in the other rocks. 
The figures obtained are set forth as in the following table : 
Anorthosite, New Glasgow, Province of Quebec, Canada. 
Size 
.99 X .99 
Area 
.981 
E 
11,960,000 
<r 
.262 
D 
8,368,000 
c 
4,750,000 
Load (in pounds). 
Longitudinal 
compression 
(multiply 
readings by 4 
for millionths). 
Lateral 
extension 
(millionths) . 
I OOO 

51 
101 
157 
212 
264 
318 
373 
328 
278 
227 
173 
116 
58 
3 
O 
41 
81 
124 
168 
214 
260 
309 
266 
222 
179 
135 
90 
44 

^.OOO. . 
5 ooo 
7 ooo 
o ooo 
II OOO 
11 OOO 
15 ooo 
13 ooo 
II OOO 
Q OOO 
7 OOO 
c OOO 
i OOO. 
I OOO . 
The averages of the values found are as follows : 
E= 11,960,000; ff= 0.262; D= 8,368,000; C= 4,750,000. 
The stress-strain curves of the rock are shown in figure 20, in which I 
represents longitudinal compression and II lateral extension. 
