466 Sayles— Dilemma of Paleoclimatolo gists. 



Mississippi, Alabama, Georgia and Florida) is 16.3 

 degrees F. The average temperature at a depth between 

 400 and 500 feet for the southern states for 31 wells was 

 73.4 degrees F. and for 25 wells in the northern states 56.9 

 degrees F. All boring records were taken at random. 

 For temperatures at depths between 900 and 1,200 feet it 

 was found that in the northern states with sixteen records, 

 the average temperature was 63.5 degrees F., and in the 

 southern states between the same depths with sixteen rec- 

 ords, the average temperature was 78.8 degrees F. Okla- 

 homa was substituted for Georgia and Illinois for 

 Nebraska as there were no records between 900-1,200 feet 

 available in Georgia and only one in Nebraska, and Texas 

 was omitted. The average mean annual air temperature 

 for the northern states was 50.4 degrees F. and 65 degrees 

 F. for the southern states. The difference between the 

 average ground temperatures in northern and southern 

 states this time was 15.3 degrees and between the air tem- 

 peratures 14.6 degrees F. In Nebraska and westward, 

 and in Texas and westward, the thermal gradients are on 

 the whole higher than in the Appalachian states. On this 

 account the states in the above list east of the Mississippi 

 River only were used in an additional test, and the differ- 

 ence between the average earth temperatures of the north 

 and south between depths of 400 and 500 feet was found 

 to be 14.9 degrees and the difference of the average air 

 temperatures of the stations 15.8. At depths between 900 

 and 1,200 feet there was a difference between the average 

 earth temperatures of only 11.9 degrees, and between the 

 average air temperatures of 15.5 degrees. A map of the 

 United States with thermal gradients plotted, resembling 

 the isostatic map recently published by Bowie, is much 

 needed. 



In Alaska and Siberia the regolith is often frozen solid 

 for many feet. From there southward the temperature 

 of the upper crust grows warmer until at the equator the 

 warmest temperatures, for a large average, are obtained. 

 Has this always been the case? 



It is probable that during the Pleistocene this condition 

 of the temperature gradients was accentuated. With a 

 removal of the polar ice and prevalence of warmer condi- 

 tions would the underground conditions of the north 

 approach the conditions found in low latitudes today F If 



