CLIMATOLOGY OF THE LATE PALEOZOIC 233 



Schuchert has stated, as noted above, that the glacial periods of the past 

 have been somewhat sudden in their onset, but if we give to the expression 

 "glacial periods" the broader meaning which should be given it, implying 

 reduction of temperature with, perhaps, accompanying aridity or semi- 

 aridity, it is not so certain that the climatic change was a sudden one. 

 Certainly the change in late Paleozoic time in North America was a slow 

 one, and its slow advent is indicated in the increasing accumulation of red 

 beds, with their suggestion of alternate seasons of drought and humidity. 

 The climatic change from the conditions of the first half of the Pennsylvanian 

 to the Permo-Carboniferous, though slow and marked by local fluctuations, 

 was a very comprehensive one, both in character and the extent of the area 



involved. 



A. CLIMATE OF THE LATE PENNSYLVANIAN. 



The most complete and dependable description of the climate of Penn- 

 sylvanian time has been given by David White,^ from whose p^per the follow- 

 ing quotations are taken : 



"The extreme range of climate and the strong demarcation of the earth's 

 climatic zones in the present day contrast strongly with the atmospheric conditions 

 that appear to have prevailed during the deposition of most of the extensive 

 coal, even in the high latitudes. Such strongly contrasting secular climatjc 

 changes as are shown to have taken place since the deposition of peat began in 

 many of our actual bogs, and as are cited as arguments for possible corresponding 

 variation of climates and vegetal types during the formation of the vastly thicker 

 peat beds from which our coals were made, are not in the slightest degree indicated 

 in the great coal beds of the older formations, and probably never occurred unless 

 in the rarest and most exceptional cases, such as possibly in connection with 

 some of the older Gondwana coal beds of Australia, India, or South Africa. In 

 no part of the world to-day are the genetic conditions of the great ancient coal 

 formations to be found, except locally and on a relatively small scale. Topo- 

 graphically, climatically, and botanically their nearest semblance is to be found 

 in coastal and near-tide-level swamps of the South Atlantic and Gulf States, the 

 great estuarine and lowland swamps of India, and the lagoons and swamps of the 

 Indo-Pacific zone of heavy rainfall. "^ 



This subject is further considered in connection with a review of the 

 evidence as to the climate attending the great coal formations. 



" Climates of the Coal-formation Periods. 

 " In the following pages is given a brief outline of evidence and conclusions 

 as to the climates characteristic in general of the periods of the great coal forma- 

 tion, with particular reference to the regions of the coal basins. It will be seen 

 that during the times of deposition of most of the principal coal groups the climate 

 has been characterized by (i) general mildness of temperature, approaching in 

 most cases tropical or subtropical; (2) conspicuous equability or approximation 



' White, David, The Origin of Coal, Bureau of Mines Bull. 38, p. 67, 1913. 

 2 Potonie, H., Ein von der Hollandisch-Indischen-Sumatra Expedition entdecktes Tropen- 

 moor. Naturwiss. Wochenschr., Jena, Oct. 20, 1907, PP- 657-666. 



