F. H. Knoivlton — Evolution of Geologic Climates. 191 



Eichmond group, that ranges from Baffinland, Alaska, 

 and Baltic Eussia south as far as Texas and India. 

 The earliest Magaran had nearly the same wide-flung 

 distribution. The earliest Devonian Helderberg group, 

 as well as the earliest Mississippian black shale beds, 

 were likewise widespread and without temperature zones. 



As near as I am able to interpret certain recent 

 remarks of Gr. E. Wieland,^ he appears to hold that much 

 of the paleobotanical data relied upon to interpret geo- 

 logic climate was based on studies of lowland floras, 

 whereas, when the highland floras are studied, if they are 

 ever available, quite another story may be told. This is 

 easily answered. Interpretations have been based on 

 floras that are actually known and not on what may yet 

 be discovered. 



To return again to some of the objections raised by 

 Professor Coleman. In discussing seasonal changes he 

 says that after admitting the presence of growth rings 

 in trees in the Pennsylvanian, Permian, Jurassic, Cre- 

 taceous, etc., I do ^^not explain how this can be reconciled 

 with the uniform and steady supply of heat from the 

 earth's interior under the assumed screen of clouds." 

 I do not recall that I ever stated that the supply of earth 

 heat was '^uniform and steady," for I entertain no such 

 view. My whole paper is predicated on a dual heat 

 supply, that from the earth itself and that from the sun. 

 The earth heat undoubtedly fluctuated from time to time 

 as evidenced by vulcanism, to use no other example. 

 When earth heat was at a maximum the cloud envelope 

 was most complete and the sun shut out, but when earth 

 heat diminished evaporation and the cloud spheroid also 

 diminished. I have quoted on this point as follows in my 

 paper (p. 541) : 



' ' As the heat carried up from the earth 's surface was more and 

 more lost by radiation into space from the exterior cloud-surface, 

 the isothermal shells would gradually descend, and the tempera- 

 ture of falling rains would become lower, so as under favorable 

 conditions to fall as snow. It is clear that snow-fall might occur 

 at any period of earth's evolution on high mountain ranges or 

 plateaus, and there the accumulations of snow might at any 

 period have formed nevees and glaciers with their well known 

 effects." 



^ Science, n. s., vol. 53, p. 437. 



