REPORT OF THE DIRECTOR I92O-2I 121 



" dreikanter " (see Walther, 1909, p. 287) and the Jotnian sand- 

 stones in Scandinavia and Finland with their ripple marks and 

 mud cracks — not to speak of a 2 -meter thick anthracite bed — 

 as proof of continental conditions; and the distinction of four major 

 unconformities in the Finnish series leaves no doubt of a series 

 of great and enormously long, complete emergences of these con- 

 tinental areas that, if they correspond to the unconformities observed 

 in North America and eastern Asia, would even indicate worldwide 

 major continental emergences. 



We see in these great unconformities of the Precambrian of North 

 America and Eurasia strong evidence that the supposed continental 

 areas responded as continental units not only to the orogenic forces 

 that folded them., but also to the epeirogenic forces- that elevated 

 them from time to time. While the continents, according to the recent 

 investigations of isostasy, are composed of positive and. negative 

 elements that owing to minor differences in relative density act 

 more or less independently, they seem nevertheless to have formed 

 units of a major grade that reacted uniformly in times of greater 

 diastrophic events. This is, at least, strongly urged by the evidence 

 of the great widely spread Precambrian unconformities that separate ■ 

 the different formations, both here and in the old world. 



The evidence of repeated periods of wide continental elevation 

 in Precambrian time that is afforded by the major unconformities is 

 . corroborated by the recognition of Proterozoic giaciation, .not only 

 on the Canadian shield as mentioned before, but also in Scotland, 

 the Baltic shield, South Africa, India, South China, South Australia 

 and Tasmania. 



The great Precambrian continental mass of the southern hemi- 

 sphere which the Precambrian folding by its continuous north-south 

 folding, indicates to have extended from Africa over Madagascar 

 to Middle Australia and East India — and if the folds, of eastern. 

 Brazil and eastern Australia are posthumous in character, also to 

 these regions — is the evident ancestor of the great Gondwanaland. 

 Gondwanaland had its most glorious geologic period in Carboniferous 

 to Triassic time when it extended, as a separate continental mass, 

 from western South America across Africa to South Asia and beyond 

 Australia. This vast continent with its characteristic flora and glacial 

 period reached in Permian time in east-west direction two-thirds 

 around the world. It broke down in the middle, where the Indian 

 ocean now is, in Jurassic time, and Africa, East India, Australia and 

 a large portion of South America are its remnants, (fig. 3 a-d) 



