MEASURING GEOLOGIC TIME— LANE 



247 



TEM PERATURE- FAH REN HEIT 



Ui Ci ^ 

 o o o 



8 g 



CD 



o — NJ w ^ cn <j> 

 ooooooooo 



1,000 



^000 



3P00 



O 

 m 

 TJ 



H 

 I 

 I 4,000 



n 



spoo 



6p00 



7,000 



8P00 



Figure 3.— Curve showing the temperatures of the rocks for various depths, increasing, but increasing 

 more rapidly at the bottom, indicating a heat wave which has not reached the bottom. (C. E. Van 

 Orstrand, On the nature of isogeothermal surfaces, Amer. Journ. Sci., vol. 15, p. 614, fig. 8, June 1928.) 



