BEARINGS OF RADIOACTIVITY ON GEOLOGY 685 



not take into consideratiion the effects of liquefaction and extru- 

 sion and these in the planetesimal view are of the first order of 

 importance. The theoretical curve mathematically deduced by 

 Dr. Lunn is, however, an indispensable basis for a third approxi- 

 mation in which the effects of liquefaction and extrusion are taken 

 into account. 



Before passing on to consider liquefaction and extrusion, it is 

 well to note that the Lunn curve based on the Laplacian law of 

 density also is low near the surface and that its rate of rise is much 

 below that of the temperature gradient observed in wells and 

 mines. Dr. Lunn, on assumptions carefully specified in his dis- 

 cussion in the paper cited, found the rise in the first 200 miles 

 only 330 C. 



This low development of heat in the outer part of the earth 

 seemed at first thought to present a difficulty of a rather serious 

 nature, but it was believed to be met by the effects of liquefaction 

 and extrusion, and these were made the chief basis of an additional 

 approximation to the actual temperature curve (Chamberlin and 

 Salisbury, Geology, I, 265-67). It was held that the rising heat 

 of the interior would reach the temperatures of fusion or of mutual 

 solution of some ingredients in the mixed material much earlier 

 than that of other ingredients, and that the ascent of the portion 

 that became molten carrying its latent as well as sensible heat 

 into the cooler outer zone would necessarily raise the temperature 

 of that zone. It was held that the continuation of this process 

 served as a constant influence tending to retard the rise of tem- 

 perature in the deeper zone where the partial liquefaction was in 

 progress while it progressively raised that of the outer zone into 

 which the liquid rock was intruded, whether it lodged in the crust 

 or passed through it to the surface. This extrusive process was 

 supposed to have continued to the present day and to have resulted 

 in a permanent adjustable working curve of accommodation 

 between thermal, fluidal, and mechanical conditions. This curve, 

 except in the cool crust, was essentially identical with the fusion- 

 Problems," Publication No. 107, Carnegie Institution of Washington, 1909, pp. 169- 

 231; for a summary and figure of curve see also Chamberlin and Salisbury, Geology 

 (1904), I, 566. 



