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tioR to that, if the heat came from the centre of the earth ; hut 

 experiment proves tliat it is not so. (See address of President 

 Geological Society for 1858.) Again, theory would say that this 

 heat would increase regularly towards the tropics, as there the 

 earth would lose less heat by radiation. Fact shows a departure 

 from this assumption. Moreover, at the Bagneres de Luchon, in 

 the Pyrenees, it was found that by boring a horizontal shaft into 

 the mountain, they came upon hotter water, and so proving that 

 it is not always an approach to the central parts of the earth that 

 involves increase of heat. If the globe has gradually cooled down 

 and formed a solid crust on its exterior, it follows that it must 

 still be cooling down, and that such cooling has proceeded steadily 

 from the time when it first began to cool, although it may well 

 be that as the crust thickens, it cools more slowly. I only state 

 that the progression must be regidar, and not subject to fits of 

 increase of heat. If we examine the geological records of the 

 past, we find that as we mount upward in time, towards the 

 commencement of our earth's history through the Pliocene, the 

 Miocene, the Eocene, the Cretaceous, the Carboniferous, the 

 Devonian, the Silurian eras, we shall find that there are numerous 

 signs that the cHmate of the globe has in these previous ages 

 been much warmer at least in Northern latitudes than now 

 obtains, and these facts taken isolated have seemed to countenance 

 the idea that the cause was the internal heat of the earth, and 

 hence an additional reason for supposing the central heat theory 

 a fact. 



But admitting the fact of the previous warm climate, I do not 

 think that the cause has been rightly interpreted. 



Let us suppose, however, that we admit the theory. We find 

 that during these periods, although there wore times when the 

 climate of the polar regions was warmer and more uniform than 

 at present, yet there were alternating periods when this state of 

 things was followed by a much greater cold than now exists, and 

 that if it be said that formerly the polar and temperate regions 



