24 AN INVESTIGATION INTO THE 
In each table there follows the values obtained for successive loadings of 
1,000 pounds in the case of each specimen, first for compression, when the 
figures multiplied by four give millionths of an inch, and then for lateral 
expansion, given directly in millionths of an inch. These afford the data for 
calculating the constants and for plotting the curves which accompany every 
table. 
In the figures for the constants of iron and of one or two of the rocks, which 
are the result of measurements which were made at the beginning of the 
investigation, a slight correction has been made, owing to the inaccurate cali- 
bration of the extensometer, which will explain a certain discrepancy which 
will appear if the figures are recalculated. 
THE ELASTIC CONSTANTS OF ROCKS COMPOSED OF A SINGLE 
MINERAL. 
MARBLES AND LIMESTONES. 
BLACK BELGIAN MARBLE, BELGIUM. 
This rock is known in trade by the name of ' ' Belgian black " or ' ' Noir fin. " 
It is an extremely fine grained black marble which takes a very high polish 
and is used very extensively in interior decoration. It has a splintery frac- 
ture, breaking almost like glass. 
When thin sections are examined under the microscope the rock is found 
to be so fine in grain that a high power is necessary to resolve it. It is 
composed of minute calcite grains from 0.02 mm. to 0.002 mm. in diameter 
and of irregular shape, between and around which are occasional minute films 
and spots of a black color. 
In this very fine grained and even groundmass are embedded a very few 
larger forms of clear white calcite, some of them rodlike, others circular in 
shape, and others possessing more complicated outlines. These are evidently 
of organic origin, representating small fragments of fossils. They are very 
sparsely scattered through the rock. The rock also contains occasional 
minute grains or crystals of iron pyrites. 
Fragments of this rock dissolve readily in cold dilute hydrochloric acid, 
giving off a fetid odor and leaving a considerable amount of a light flocculent 
residue, black in color and apparently consisting of some form of bituminous 
matter. In the residue there are also a few minute grains of pyrite. 
Plate I A is a color-process photograph of a polished surface of this marble 
and Plate I B is a photomicrograph of a thin section of the rock, taken in 
ordinary light and magnified 27 diameters. 
A square prism of the rock of the usual dimensions was employed to meas- 
ure the elastic constants, and the results are set forth in the table found 
on page 25. 
