GEOLOGY 



THE AGE OF OUR PLANET. 



Monsieur Boue, of Vienna, (Austria,) communicated to the G^n- 

 logical Society of France, some memoranda of a book just published by 

 N. Unser, "The History of the Vegetable ^Vorld." 



In it there are some considerations respecting the age or antiquity 

 of the earth, drawn from its rate of cooling. 



It is supposed that the plants of the coal period required a tempera- 

 ture of 22 Reaumer. The mean is at this time 8, or. 14 less. 



By experiments on the rate of cooling of lavas and melted basalt, it 

 is calculated that 9,000.000 of years are required for the earth to lose 

 14 Reaumer. 



M. Hibert puts the period at 5,000,000. But supposing the whole 

 to have been in a molten state, the time that must have elapsed in 

 passing from a liquid to a solid state, is fixed at 350,000,000 years. 



CENTRAL HEAT OF THE EARTH. 



Prof. William Hopkins, President of the British Association, in his 

 annual address, notices the above subject as follows. One favorite sub- 

 ject of speculation in the physical branch of geology has been, at all 

 times since the origin of the science, the state of the interior of our 

 planet, and the source of the high temperature observed at all con- 

 siderable depths beneath its surface. The terrestrial temperature at a 

 certain depth in each locality (about 80 feet in our own region) remains 

 constant during the whole year, being sensibly unaffected by the 

 changing temperature of the seasons. The same, of course, holds true 

 at greater depths ; but the lower we descend the greater is this inva- 

 riable temperature, the increase being proportional to the depth, and 

 at the rate of 1 Fahr. for about every 60 or 70 feet. Assuming this 



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rate of increase to continue to the depth of 50 miles, we should arrive 

 at a temperature about twice as great as that necessary to fuse iron, 

 and sufficient, it is supposed, to reduce nearly the whole mass of the 

 earth's solid crust to a state effusion. Hence the opinion adopted by 

 many geologists is, that our globe does really consist of a solid shell, 

 not exceeding 40 or 50 miles in thickness, and an interior fluid nucleus, 

 maintained in a state of fusion by the existing remains of the heat to 



