1 88 F. H. KnowUon — Evolution of Geologic Climates. 



of fossils will probably have to agree with Knowlton that the 

 biotic evidence, and chiefly that of the floras, does in general bear 

 out his conclusion that 'climatic zoning such as we have had 

 since the beginning of the Pleistocene did not obtain in the 

 geologic ages prior to the Pleistocene. ' ' ' 



Let us take first the question of so-called ^'ice ages/^^ 

 I have freely admitted that there are evidences of refri- 

 geration at a dozen or more points in the geologic column 

 between Huronian and Eocene, but I have questioned 

 whether more than three of them as at present known 

 are entitled to be called '4ce ages/^ Coleman says: 



''The presence of great ice sheets in Australia, South Africa, 

 South America, and India, as admitted by Knowlton himself , is 

 fatal to the theory he advocates, and no suggestion that the period 

 of cold was short affects the conclusion. ' ' 



If it could be proved that the glaciation on these conti- 

 nents took place mth earth temperatures under solar 

 control as Professor Coleman appears to believe, it would 

 indeed be fatal to the theory I have advocated, but this has 

 not yet been demonstrated. Glaciation in or adjacent 

 to the tropics at or near sea-level, as attested by inter- 

 bedded marine deposits, is to my mind impossible under 

 the rays of a vertical sun ! 



The Pernio- Carboniferous glaciation is one of the 

 unexplained mysteries of geology, someone has said, and 

 with the assumption of solar control this is undoubtedly 

 true, but with the predication of dual heat supply it can 

 be and is explainable. 



The manner in which this principle is applied is ex- 

 plained at length in my paper and need not be here 

 repeated. It is an explanation that has at least the 

 merit of explaining certain phenomena that are matters 

 of common knowledge and observation that obtrude in 

 studies of geologic climates. It will be noted that nowhere 

 in my paper has it been denied that there are repeated 

 evidences of refrigeration, and it is more than likely that 

 others may be discovered, but my main contention is that, 

 with the exception of possibly three (Huronian, Permo- 

 Carboniferous, Pleistocene), there is to my mind no 

 adequate evidence available that they were more than 

 local, and without mdespread effect on temperatures, 

 distribution of life, etc. , This linking up of isolated 

 localities all over the world without adequate age-deter- 

 mining data seems to me to be unwarranted. 



