Sayles — Dilemma of Palepclimatolo gists. 167 



so, would not the earth give much more heat to the waters 

 in a warm period than at such a time as the present when 

 the earth is evidently still cooled by glacial conditions and 

 has not yet gained back its warm period heat! 



Now let us again consider the rocks under the bottoms 

 of the oceans. If the temperatures of the outermost crust 

 are controlled to the extent indicated above by the temper- 

 atures of the air, the temperatures of the rocks below the 

 oceans should also be controlled by the bottom waters of 

 the oceans. In other words, these rocks should be cooled 

 to a temperature of about 32° F., for an unknown depth 

 below the bottom. The evidence gathered from geother- 

 mal gradients along the coasts does not point to such a 

 conclusion, nor does the evidence of a rise in the tempera- 

 ture near ocean bottoms, as discovered by Murray, indi- 

 cate such cold sub-oceanic rocks. 



It has been said that a drop in the mean annual tempera- 

 ture of 10-15 degrees F. would bring on a glacial period. 

 This would not apply to one of the warm periods. To 

 change one of the warm periods into a glacial period a drop 

 of something between 30-40 degrees F. might be necessary. 

 It would almost seem that nothing but land emergence 

 could cool off the earth enough to prepare the way for 

 glacial conditions, and furthermore, large continental 

 areas are necessary for large continental glaciers, such 

 as are recorded in some of the tillites of the past. If the 

 sun should change its heat or if volcanic ash filled the 

 upper air during a period of great ocean transgression no 

 glaciers of great extent could form, so it is only during 

 periods of land emergence that great continental glaciers 

 could register their existence in the rocks. Croll 20 men- 

 tioned many strata barren of organic remains and 

 inferred from this cold periods intercalated between 

 warm periods. These cases may be doubtful, but the 

 inference has not been proved wrong. To change the 

 temperature of the earth from what it was during the 

 warm periods to a condition cold enough for a great ice 

 sheet would mean a very great change. 



If the waters and lands of the past were universally 

 warm over the earth without very marked zonal arrange- 

 ments of temperature, as most of the paleontologists and 

 paleobotanists would have it, the waters no doubt con- 

 tributed largely to this condition. According to Mur- 



