.210 Frank Carney 



surfaces similarly altered during the recent ice age. Weathering 

 and erosion have locally removed the conglomerate, revealing 

 the scored and grooved rock surfaces beneath. 



Detailed studies in Australia show that the Permian glacial 

 period there was complex, in that the ice did not make an advance 

 and then disappear, but there were several readvances, spaced by 

 warmer conditions, producing in succession till and shale, separa- 

 ted by other deposits. Coal beds are found in some of these inter- 

 glacial periods. Furthermore, the flora of the horizons itself 

 reflects glacial climatic conditions. 



Much speculation is possible on the basis of these three widely 

 separated regions containing glacial conglomerates of the same 

 age. Did all three belong to an extensive land area occupying the 

 position of the Indian ocean? Whatever may have been the associ- 

 ation or disconnection of these three distant tracts, it is certain 

 that climatic conditions very unlike the present then existed. 

 The Indian glaciated area lies near and north of the equator; the 

 Australian region, not very far south ; while the African is a little 

 farther awa}^ Possibly in the Permian ice sheets there is a sug- 

 gestion as to the cause of glacial periods. Unless we can prove 

 marked shifting in the location of the poles, it must be accepted 

 that glacial conditions can exist in the tropical belt. 



In South America, glacial conglomerate belonging to the Per- 

 mian period has been studied. The matter has recently been 

 under investigation, but the reports of the work are not yet avail- 

 able. 



Conclusions. With four well established times of glaciation 

 scattered through the geologic scale, it would appear that glacia- 

 tion is a normal, not an abnormal feature in earth-history. When 

 men labored under the idea that there had been only the one gla- 

 ciation, it was interpreted as an abnormal condition. Whether 

 these four periods are rhythmically spaced, we do not know. 

 Man has not yet learned how to measure geologic periods. We 

 merely feel that the Permian is very much nearer the present than 

 is the Cambrian ; but this gives us no definite conception. 



Professor Chamberlin, who has most convincingly explained 

 the carbon-dioxide and water-vapor cause of glaciation, has shown 

 how the past glaciations may be a normal feature of earth-history. 

 Briefly the explanation is this: With continued base-leveling of 

 land areas, the epicontinental parts of the seas were broadened 



