ELASTIC CONSTANTS OF ROCKS- 33 
The elastic constants of the rock were measured on two round columns, 
four measurements of vertical compression and two of lateral extension being 
made. The results are given in the table on page 32. 
The averages of the results obtained are as follows: 
"=9,205,000; ff= 0.2522; D= 6,167,500; C= 3,636,000. 
The difference between the highest and lowest readings for D is 660,000' 
The results of the measurement of specimen a are shown in graphic form in 
figure 10. I represents longitudinal compression and II lateral extension. 
THE ELASTIC CONSTANTS OF ROCKS COMPOSED OF MORE THAN 
ONE MINERAL. 
ACID PLUTONIC ROCKS. 
GRANITE, BAVKNO, ITALY. 
This well-known granite is pale pink in color, and although coarser in grain 
than the rocks just described, is a granite of medium grain and is very uniform 
in character. It resembles the Lily Lake granite closely in appearance, 
although it is a little finer in grain. 
It is composed essentially of quartz and orthoclase, with very small pro- 
portion of biotite; the biotite is in places somewhat altered to chlorite, and 
the orthoclase is in places somewhat turbid from the presence of kaolin, but 
the rock may nevertheless be characterized as a very fresh one. 
It has a typical hypidiomorphic granular structure. The orthoclase often 
shows faint microperthitic intergrowths, and some plagioclase is present as 
an accessory constituent. The quartz usually shows a very faint undulatory 
extinction, although this is in some cases quite distinct. 
A color-process photograph of a polished surface of the rock is shown in 
Plate VI A, and a photomicrograph of a thin section of the rock is shown in 
Plate VI B. The latter was taken between crossed nicols in polarized light 
and is magnified 30 diameters. The crack seen crossing the rock in the 
photomicrograph was developed during the grinding of the thin section 
and does not indicate any shattering or lack of continuity in the substance 
of the rock itself. 
Four round columns, b, c, d and e, were employed in the measurement of the 
elastic constants of this granite. On specimen b a double set of measure- 
ments was made in each of the planes U and P, which planes were at right 
angles to one another. In the case of column c two sets of measurements were 
made in two planes, also at right angles to one another (referred to as "first 
