62 Geological Society. 



*' were deposited in succession, the Temperature seems to have been 

 4< still further lowered, and to have continued to diminish gradually 

 " even after the appearance of a great portion of existing species upon 

 " the earth." The little knowledge we have of the fossil productions 

 of countries south of the temperate zone, induces me to believe that 

 these observations are as applicable to the southern hemisphere as to 

 the northern. 



This Refrigeration, one of the most undoubted facts in geology, is 

 supposed by the Huttonians, and if I mistake not, by M. Elie de Beau- 

 mont and others, to arise from a decrease of the Central Heat j an 

 opinion, however, which cannot, I think, be supported. 



We know of one method only by which Central Heat, if it exists, can 

 pass from the earth, viz. by Radiation. It cannot pass by Conduction. 

 Conduction implies conductors, which in empty space are not to be 

 procured *, but the Radiation of heat, at low temperatures, is so slight 

 that it is scarcely sensible at 100° of Fahrenheit's thermometer, 

 a temperature twice as great as the medium temperature of the sur- 

 face of the globe at this time. The Temperature of the earth's surface 

 has been shown by Fourier to be as constant as are the dimensions 

 of its orbit, and the period of its annual revolution. Laplace observes, 

 that our planet has undergone no- Contraction of Size during the last 

 2000 years ; consequently there has been no sensible Refrigeration 

 during that period, and the last Seculum of M. de Beaumont has 

 already extended to more than twice the length of a Millennium. 



Another argument, or rather postulate, has been adduced in fa- 

 vour of Central Heat, — the Fusion of Unstratified Rocks, and their 

 forcible Injection into the Stratified. 



Gentlemen, I have confessed to you again and again, that I am not 

 aware, nor has any one as yet informed me, by what test Stratified 

 and Unstratified rocks can be distinguished ; the only test I know is 

 the good will and pleasure of those who make the distinction. The 

 followers of Pluto seize and appropriate to his use as many rocks as 

 they think proper. By virtue of such seizure, these Rocks become ne- 

 cessarily Unstratified : why so ? because if Stratified they would be no 

 longer Plutonic. Stratification I know is a question to be determined 

 not by the senses but by the fancy j otherwise, I would say, that the 

 magnificent range of basaltic cliff, which extends from the county of 

 Derry along the coast of Antrim as far as Fairhead, is as distinctly 

 stratified as any mountain-limestone, oolite or chalk in Great Britain. 



However, I waive this objection as it leads me away from my sub- 

 ject, and return to the consideration of Central Heat. Have those 

 who believe in this agent ever taken into their account the nature 

 of the substances said to have been fused ? Many of the trap rocks, 

 not all of them, (for the family is large, and many of its members have 

 been introduced into it, not by nature but by adoption,) I attribute 

 to the agency of the causes which have produced lava, causes which, 

 comparatively speaking, I do not believe to be very deep-seated. 



• See Comparative View of the Huttonian and Neptunian Systems of 

 Geology. 



