temperature of the interior of the earth. 1 1 1 



that the temperature of mines and deep cavities uniformly in- 

 creases as the depth from the surface increases ; in proportions 

 somewhat varying, indeed, but calculated on an average at about 

 one degree of the centigrade thermometer for each thirty or 

 forty metres, (ninety-one, to one hundred and thirty-one English 

 feet.) 



"Hence, the conclusion has gradually prevailed that the earth 

 possesses a central heat of its own, and an internal igneous fluid- 

 ity that takes date from the very commencement of the exist- 

 ence of our globe : that the crust of the earth has gradually been 

 hardened by radiation and molecular communication of caloric 

 from stratum to stratum." 



How long it has taken to produce this gradual coolness 

 and consolidation of the present crust of the earth, we have 

 not the means of conjecturing in the present state of our 

 knowledge. 



" La Grange and Dolomieu were the first who returned to 

 the old theory of central heat. Hutton, and his commentator, 

 Playfair, followed. Lately, M. Fourier, in his Researches res- 

 pecting the general theory of heat, was led the same way. The 

 subject was also taken up by the much lamented M. de la Place." 



The publication of M. Faujas de la Fond on the extinct 

 volcanos of Viverais and Velay, the account of central 

 France by M. Giraud de la Soulavie, and the elements of 

 geology by M. Breislak, have added strength to the modern 

 theory. In England, Mr. Kirwan and Professor Jameson 

 adopted Werner's theory ; but Hutton and Playfair, Grego- 

 ry Watt and Sir James Hall, the disciples of Hutton, Sir 

 George M'Kenzie, Dr. M'Culloch, Mr. Conybeare, and Mr, 

 Scrope, have greatly contributed to change the geological 

 opinions of the British public in this respect. At present the 

 igneous fluidity of the central mass of our earth, and the ig- 

 neous origin of floetz trap, may be regarded as the settled 

 theories both of the British and continental geologists. Wer- 

 ner seems to have suspected the untenable character of his 

 own opinion as to the aqueous origin of the floetz trap for- 

 mation, when, being at Paris, he refused the pressing invita- 

 tions to visit Auvergne. 



" If the proofs hitherto adduced in favor of central fusion be 

 sufficient, we ought to consider this theory as fully established : 

 if not, further experiments ought to be instituted that shall set 

 the question beyond reasonable doubt. 



