54 The Causes and Phenomena of Earthquakes . 



peratui'e of boiling water would be reached at If mile of depth, 

 whilst in the deepest English shaft, that of Duckinfield, the depth 

 would be 2j miles. Whilst, then, it is certain, that there is no 

 normal depth equivalent to a degree, we have yet by these new 

 researches a confirmation of a fact closely in relationship with 

 the theory of a fluid zone of molten matter on which, the crust of 

 the earth is floating. Details of experiments of this kind are 

 sufficiently numerous in scientific records, and works of popular 

 geology give numerous results There is a very useful paper on 

 this subject, in the 17th number of the Journal of Science, by my 

 friend Mr. Hull. But it has to be noticed, that the proximity of 

 a volcano has no necessary connection with this phenomenon, for 

 the temperature of the well of Grenelle, at Paris, (1794 feet 

 deep) is 82°, and that of Salzwerk, iu Germany, (at a depth of 

 2281 feet), is 91°, whilst the Bath waters in England, rise with a 

 temperature of 117°, and a spring at Arkanzas, in America, has 

 that of 180° F., both probably proceeding from depths far below 

 those of Paris and Salzwerk. Similarly, on the Flinders Biver 

 in North Australia, where there is no immediate volcanic influence, 

 there are springs which issue with a temperature of 107° F. On 

 the other hand, it is recorded, that the deepest point to which the 

 skill of man has penetrated, is the Pit Simon, at Gilly, near Char- 

 leroi, in Belgium, which is 3489 English feet in depth, and the 

 temperature of it is only 7S°8 F., whilst at the colliery of Grand 

 Mombourg, at Montigny, at a depth of 2180 feet, the temperature 

 was only 50 F., and at 1922 feet, 72°5 F. Should this be due to 

 the temperature of the air, it will show how carefully experiments 

 ought to be conducted if truth is to be arrived at. 



That this internal heat has nothing to do with astronomical 

 causes, has been satisfactorily shown by Sir John Herschel, in his 

 paper in the Transactions of the Geological Society (2ud ser. vol. 

 in.), read 15th December, 1830, in which he demonstrates that 

 the causes of changes of climate in ancient periods must be 

 sought elsewhere than in the relations of our planet to the system 

 to which it belongs. 



In a very elaborate discussion by Mr. Hopkins, that author 

 points out that though the precession and nutation of sun and 

 moon might exhibit alteration from their present condition, if the 

 the earth's crust were much thinner, than it is believed to be ; 

 yet. as it is, it is not subject to influences from these astronomical 

 conditions Nevertheless, Herschel admits that the sun and moon 

 have a tendency to produce a tide in the solid strata of the earth, 

 and would, were the crust fluid ; as there is an influence in a 

 tangential direction, causing a strain in the crust when the sun is 

 on the horizon, and a pressure under the zenith. Still, all this 

 does not affect the proposition, that the phenomena of volcanos 



