ORIGIN OF ERUPTIVE AND PRIMARY ROCKS. 317 



" lxxxi, 562) a series of experiments from which it appears 

 " that the temperature of the fusing point of various substances 

 " increases with pressure. These experiments have it is true only 

 ** been made on two easily fusible organic substances, spermaceti 

 " and paraffine. The melting point of the former is under a 

 " pressure of 100 atmospheres raised 2.1° Centigrade, while that 

 " of paraffine is raised 3.6° Centigrade. It cannot be doubted that 

 " a heavy pressure acts in a similar manner, although possibly not 

 " to such an appreciable extent, upon solidifying masses of silicates. 

 " If the point of fusion of the latter, under a pressure of 100 atmos- 

 " pheres, only increased 1° Centigrade, this would still be sufficient 

 " to explain many important points in geology, and especially in 

 " the formation of crystalline rocks. Although the law of the 

 " dependance of the point of fusion upon pressure is far from 

 " being known, the observations of Bunsen already mentioned 

 " have incited me to enquire as to what pressure, on the basis of 

 " the increase of density already mentioned, may be expected to 

 " exist at any given point in the interior of the earth. If we 

 " imagine the whole globe to be in a fluid condition, the following 

 " pressures would be experienced at the respective depths men- 

 " tioned. 



Depths in miles. Pressure in atmospheres. 



34 17138 



68 34591 



103.. 53070 



137 72195 



171 92432 



206 113180 



240 , 134660 



274 156840 



309 1 79680 



343 203320 



686 471680 



1029 786080 



1372 1125690 



1716 1468000 



2059 ... 1 701500 



2402 2297500 



3088 2441900 



3432 2492600 



" If it is the case that the fusing point of metals (of which un- 

 " doubted ly the greater part of our planet consists,) increases with 

 " increasing pressure, then the question arises as to whether under 



