OF GEOLOGICAL DYNAMICS. 99 



results calculated from conduction at only the 

 present rate, giving a limit of twenty or thirty 

 thousand million years, in a short article (p. 6 

 above) of more recent date entitled, " The Doc- 

 trine of Uniformity in Geology Briefly Refuted," 

 from those of the analytical investigation of the 

 " antecedents " of the present condition of un- 

 derground heat, contained in my former paper 

 ("Secular Cooling"). The analytical investiga- 

 tion shows the law of the greater rate of con- 

 duction outwards in past times, and demonstrates 

 a much closer limit for the whole time during 

 which the earth has been solid and continuously 

 cool enough at its surface to be habitable with- 

 out break of continuity to life, than can be 

 estimated without taking into account the de- 

 viation from uniformity which I assert. 



20. Referring partly to my views and partly to 

 his own inadvertent misstatement of them Professor 

 Huxley continues : 



" Nevertheless it may be urged that such affirma- 

 " tive answers are purely hypothetical, and that 

 " other suppositions have an equal right to consid- 



H 



