ELASTIC CONSTANTS OF ROCKS- 
45 
tains a considerable percentage of microcline and of a plagioclase of the 
soda-lime series. The mica is relatively more abundant than in the other 
granites described in the present paper. The quartz shows marked undu- 
latory extinction and in some cases even an incipient granulation. The size 
of the grain of this rock is intermediate between that of the Westerly and 
the other granites, which latter are themselves about equally coarse. 
The elastic constants were measured on three square prisms, four sets of 
measurements of vertical compression and three of lateral extension being 
made. The results are given in the following table: 
Granite, Stanstead, Province of Quebec, Canada. 
No 
a 
b 
b 
d 
a 
b 
d 
Size .... 
. 954 X . 95 
1.015X1.0009 
1.015 X 1.00098 
1.0083 X .957 
.954 
1.015 
.957 
Area 
.906 
1.016 
1.016 
.965 
Side 
U. 
P. 
E 
6 000 000 
5 030 000 
5,540,000 
6 1 70 000 
IT 
.253 
.251 
.282 
.248 
D 
4 040 000 
3 360 000 
4,250,000 
4,110,000 
C 
2,395,000 
2,015,000 
2,155,000 
2,470,000 
Longitudinal compression (multiply readings by 4 for millionths). 
Lateral extension 
(millionths). 
Load (in 
pounds). 
1,000 
O 



O 
O 
O 
2,000 
70 
58 
75 
60 
29 
30 
40 
3,000 
135 
122 
145 
125 
61 
70 
80 
4,000 
200 
190 
200 
1 80 
105 
125 
119 
5,000 
250 
250 
245 
230 
149 
1 80 
155 
6,000 
310 
310 
305 
280 
200 
230 
195 
7,000 
360 
370 
350 
325 
246 
280 
235 
8,000 
415 
430 
395 
375 
295 
335 
275 
9,000 
460 
490 
445 
420 
355 
400 
320 
8,000 
430 
440 
385 
320 
340 
295 
7,000 
385 
380 
.... 
340 
275 
290 
265 
6,000 
330 
315 
.... 
295 
230 
250 
230 
5,000 
280 
255 
250 
189 
190 
200 
4,000 
2 2O 
195 
.... 
200 
140 
130 
1 60 
3,000 
1 60 
125 
.... 
140 
90 
70 
110 
2,000 
90 
60 
80 
45 
20 
50 
1,000 
IO 
10 
5 
2 
-5 
-6 
J 5 
The averages of the results obtained are as follows : 
= 5,685,000; <r = 0.2585; D= 3, 940,000; C= 2, 258,700. 
This rock, as will be seen, has a low modulus of elasticity, and like other 
rocks of which this is true, the lateral extension varies considerably in different 
specimens and the rock does not come readily to a state of ease. This is seen 
