108 FRANK D. ADAMS 
carried out in the Testing Laboratories at McGill University, a 
roo-ton Wicksteed machine being employed, and gave the follow- 
ing results: 
40,600 mee per square ne 
28,400 ‘f 
29,635 
335788 
32,750 
Average = 32,980 
The average crushing strength of the Solenhofen limestone is, 
therefore, 32,980 lbs. per square inch. It is thus seen to be an 
extremely strong rock; stronger, in fact, than an ordinary granite 
under compression. 
Four experiments were first made with columns of Solenhiofen 
limestone, the pressure being increased in each successive experi- 
ment so as to represent successively greater and greater depths 
within the earth’s crust, the element of time being also varied. 
These experiments were all, however, conducted at the ordinary 
temperature. The results are shown in Table I on p. tog. 
It will be seen from these experiments, that at the ordinary 
temperature no trace of movement could be detected in the rock 
at a pressure equivalent to a depth of 15 miles below the earth’s 
surface, even after the pressure had been continuously applied 
for two and a half months. When, however, the pressure was 
increased to that which is supposed to exist within the earth’s 
crust at a depth of 20 miles below the surface, the experiment being 
continued for two and a half months, a certain movement was 
observed. At a pressure representing a depth of 30 miles and to 
a still more marked extent at a pressure equivalent to a depth of 
4o miles, movements had taken place in 7 hours which resulted in 
the partial filling of the holes passing through the column. As 
will be noted, a depth of 31 miles represents a pressure of 100 tons 
to the square inch. 
It is thus seen that Solenhofen limestone at the ordinary tem- 
perature and under conditions of cubic compression—which are 
the conditions of pressure to which it is subjected in the earth’s 
= ee 
