Continental Drift - Snider (1858) 



Continental Drift - Du Toit (1927) 



Wandering Poles 



Interest in theories of continental 

 drift has been recently aroused 

 by modern paleomagnetic measure- 

 ments giving estimates of possible 

 different positions of the poles in 

 past geological periods. When rocl^s 

 are laid down they are magnetized 

 in the direction of the Earth's 

 magnetic field. By measuring the 

 direction of magnetization of 

 rocl^s of different ages, we can 

 determine past positions of the 

 Earth's axis, assuming, as is most 

 probable, that the magnetic poles 

 have always been aligned with the 

 Earth's axes of rotation. 



Extent of Carboniferous Glaciation 



Wandering Continents 



There are a number of controversial 



theories of continental drift. 



Taylor considered the land masses as 



having moved away from the poles 



toward the Equator. Wegener described 



the westward drift of continents 



as "ships of sial ploughing through 



a sea of sima." Du Toit based the 



fitting together of the east coast 



of South America and the west coast 



of Africa on evidence provided by the 



shapes of the coast lines. In 1944 



Holmes investigated glacial 



climates in the Southern Hemisphere, 



particularly in the late Carboniferous, 



and came to the conclusion 



that the continents had moved. 



"f^ 1%^*^ 



\. r" 



Evidence of glaciation, particularly 

 during Carboniferous times, shows 

 that during this period similar 

 ice sheets spread across 

 Argentina, south and east Africa, India, 

 and south Australia. This is diflicult 

 to account for unless we suppose that 

 the regions were once joined together - 

 far south of their present position - 

 forming "Gondwanaland." When the 

 land masses separated, the South 

 Atlantic Ocean, Indian Ocean, and that 

 part of the Southern Ocean lying to 

 the south of them were formed. 

 The periphery of Gondwanaland is 

 indicated by fold mountain ranges, 

 some with associated oceanic deeps - 

 Including the Andes of South 

 America, the Himalayas, and the 

 Southern Alps of New Zealand. 



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