82 PRINCIPLES OF STRATIGRAPHY 



the movement being northward and the ice reaching sea-level. The 

 evidence of Permo-Carbonic glaciation is even more firmly estab- 

 lished. This has been recognized in India, Australia and Tasmania, 

 South Africa (Dwyka conglomerate and tillite) and South Amer- 

 ica. In India the indications of glacial occupancy have been traced 

 from lat. i6° or 17° to lat. 34° or 35°, and in Australia from lat. 

 20° 30' to lat. 43° S. In the eastern Urals of Russia a Permic 

 boulder conglomerate suggests glacial origin (Karpinsky) and a 

 conglomerate of similar age in England has been regarded by Ram- 

 say as glacial, though this has been disputed by others. In Prince 

 Edward Island (F. Bain-3), Colorado (Cross), and eastern Mas- 

 sachusetts (Shaler) conglomerates of this age occur, which sug- 

 gest a glacial origin. In the Antarctic region glacial deposits of 

 this age have recently been found in the Falkland Islands (Halle- 

 41:264). 



It is a remarkable fact that a center of Permic glaciation in the 

 Old World seems to have been near the tropics, perhaps in the In- 

 dian Ocean (the old Gondwana land), for the movement in South 

 Africa seems to have been southward, and in India northward, the 

 movement in both cases being away from the equator. The evi- 

 dence of transported rocks in eastern Massachusetts is, however, 

 from the north and similar in extent to that of the Pleistocenic 

 glacial transportation. So far as the evidence goes, a general re- 

 frigeration of the climate of world-wide extent may have occurred, 

 and the development of an ice sheet in the tropics may be in part 

 due to the great elevation of the land of that- time and in part to 

 the nature of supply of moisture to feed the ice sheet. (Philippi- 

 75.) For another suggested explanation, see Chapter XXIII. 



Rhythm of Climatic Changes. 



The course of climatic changes during geologic time passes from 

 a rhythmically pulsating state, a climatic "strophe," to one of rela- 

 tive torpidity, the climatic "interstrophe." (Huntington-51 tjd^.) 

 The pulsations of the strophe comprise a series of accentuations of 

 certain climatic characters, such as glacial, fluvial, vegetal (when 

 plant life spreads widely), or pluvial (when much rain falls). Each 

 accentuation forms an arsis of the climatic strophe, the time of such 

 accentuation being an arsial epoch. The thesis, or thesial epoch of 

 the strophe, is the depression between the accented epochs, as in 

 the case of interglacial or interfluvial epochs, intervegetal or inter- 

 pluvial epochs. The growth in strength of the arses and theses of 

 the strophe is a gradual one to the point when the acme is reached, 



