460 Sayles — Dilemma of Paleoclimatolo gists. 



climate than we had any idea of 20 years ago, is becoming 

 evident from the discoveries of tillites all over the world, 

 to say nothing of the mass of evidence for arid conditions. 

 Is it necessary to conclude that there were no seasons dur- 

 ing all this tremendous lapse of time, or to say that there 

 were times when seasons were not pronounced enough to 

 make their mark, and at other times sufficiently pro- 

 nounced to manifest themselves with or without glacia- 

 tion? If they were not marked enough to show them- 

 selves in any manner who can say that Manson is not right 

 for such periods ? 



In spite of all the accumulating evidence for seasons in 

 the immediate and distant past, Knowlton and Manson 

 have stimulated an inquiry about earth heat which, let us 

 hope, will not cease until the matter is settled beyond all 

 question. They have courageously stated their views and 

 brought a new viewpoint in this field of past climates. 

 Under the false idea that this earth started hot and has 

 ever since been growing cold, geologists have tried to 

 explain the reason, or reasons, for the glacial periods. 

 Now that the evidence points to the idea that the earth is 

 a self -heating body mainly under the influence of pressure 

 and radioactive substances, and that there is no evidence 

 in the rocks that the first stages of the earth were very 

 hot, is it not just as important to explain such surface 

 temperatures as must have existed when warm weather 

 plants and corals thrived near the poles, as to try to find a 

 cause or causes for glacial periods ? No efforts have been 

 put forth in this direction commensurable with the efforts 

 expended on the glacial periods. It is about time that 

 geologists face about and overcome a great difficulty that 

 has not been fully recognized as a difficulty, so crystal- 

 lized has become our opinion that the surface tempera- 

 tures of the earth during the warm periods were explained 

 by the Nebular Hypothesis and the heat of the sun. Such 

 is not the case if the Nebular Hypothesis be rejected, and 

 the more thought given to this subject, the more difficult 

 does it become to explain the conditions of those times. 

 Before the solution of the glacial climates is accomplished, 

 the conditions of the heat supply of the warm periods 

 must be understood, and perhaps the glacial question will 

 then settle itself. 



What part of our surface temperature is due to the sun 

 and what part is due to our own heat? This question has 



