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IV.—On the Effect of the Glacial Period in Changing the Underground Temperature Gradient
Published online by Cambridge University Press: 01 May 2009
Extract
In his recent work on “Controverted Questions of Geology” (p. 159), Professor Prestwich remarks that the intense cold of the Glacial period may still be perceptible in the underground temperature gradient; that “to a certain depth the rate of cooling is now abnormally slow, owing to the excessive refrigeration the crust then underwent.” The suggestion is a valuable one, and I propose to test it in the present paper by estimating roughly the change which the temperature gradient may have experienced since the close of the Glacial period.
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References
page 356 note 1 This is the average of the annual means at 57 stations given by Dr. A. Buchan in his great work on “Atmospheric Circulation,” “Challenger” Reports, Physics Chemistry, vol. ii, pp. 196–199.Google Scholar
page 356 note 2 Phil. Mag., vol. vii, 1879, p. 385.Google Scholar
page 358 note 1 The calculations are performed as follows:—If b be the rise of mean annual temperature at the surface in degrees, k the conductivity of rock expressed in terms of its own capacity for heat, t the number of years since the change of temperature took place, then the change of gradient is b ÷ 
(Rev. O. Fisher, Phil. Mag., vol. xxxiv, 1892, p. 339). This value, it should be remarked, is independent of the previous gradient. Taking Lord Kelvin's value for k, namely 400, the above formula becomes. 
If b=20 and t=10000, 
and the change of gradient is ·00564 degree per foot. But the gradient now is taken to be ·02 degree per foot, so that, at the end of the Glacial period, it must have been ·02564 degree per foot, or one degree in 39 feet.
page 359 note 1 The gradient due to the temperature of solidification, the surface temperature having remained constant ever since.