The Interior of the Earth 



' But these melting points certainly do not 

 remain unaltered at the enormous pressures to 

 which the internal rocks are subjected by the 

 weight of super jacent material; at a depth of 

 forty-four miles the pressure must reach nearly 

 20,000 atmospheres. As such pressures have 

 I never been obtained in a laboratory we do not 

 know how they might affect the properties of 

 matter. It is, however, highly probable that 

 they would not raise the melting temperature 

 more than 400 or 500 centigrade. 



According to the determinations of the 

 Geological Survey , diabase, which under normal 

 conditions melts at 1170 centigrade, would 

 reach its melting point under a pressure of 

 10,000 atmospheres only at 1420, on the assump- 

 tion that the melting point continues to alter 

 at these high pressures at the same rate as at 

 lower pressures ; but other experiments show that 

 the rate of progression declines with the increase 

 of the pressure. 



Taking into consideration all these experi- 

 mental results we may conclude, with some 

 degree of probability but not of certainty, that 

 the rocks forming the lowest solid bed of the 



