REPORT OF THE DIRECTOR I920-2I 123 



Clarke (1913; 191 9) has shown that Gondwanaland existed in 

 Devonian time, but was then connected with Antarctica, and has 

 therefore proposed the name " Falklandia " for this earlier continental 

 mass (1919, p. 103). 



The evidence from the uniform direction of the Precambrian folds 

 proves, in our view, that like the two northern continental segments, 

 also the southern unit Gondwana was inherited from Precambrian 

 time and persisted throughout Paleozoic time; for the Cambrian, 

 Ordovician and Silurian periods were clearly such of land and of 

 epicontinental seas over the three southern continents. This is 

 indicated principally by the total absence of their rocks over most 

 of these three. continents of today; or where the rocks are present, 

 by their fossil and lithic facies. Parts may have been temporarily 

 invaded, as central Australia and a large part of the present Indian 

 ocean, during Cambrian time (see Schuchert, 1916, p. 98), but 

 such facts as the distribution of the Gangamopteris (Glossopteris) 

 flora together with the widely spread glacial beds call for a vast 

 Permian continent extending from South America to Australia 

 (see Kayser, 1913, p. 276). 



We believe to have advanced, in the preceding chapters, evidence 

 from at least three mutually independent sources that there 

 undoubtedly existed, at the end of Precambrian, and quite surely 

 also far back into Archean time, three immense tracts of super- 

 continental size upon the earth that behaved like continental seg- 

 ments or units in their reaction to orogenic and epeirogenic diastrophic 

 forces, to marine invasions and in the character of their sediments. 

 We have in the preliminary paper (1919, p. 5) designated these tracts 

 as arch-continents to indicate their ancestral relation to the later and the 

 present continents. In order to emphasize more fully this important 

 relation and at the same time give expression to these differences 

 in size and outline that distinguish them from their Paleozoic 

 descendants, we propose to add the prefix " Arch " to the names of 

 the continental masses which later appear in their place. We will 

 then have the three primeval continental masses of Arch-Eurasia, 

 Arch-America and Arch-Gondwana. Each of these arch-continents 

 contains certain nuclei or shields, which are positive elements that 

 remained undisturbed from later folding and more or less also from 

 transgressions. These are the Baikal shield or the ancient Angara- 

 land of Asia, the Baltic shield of Europe and the Laurentian shield 

 of America. Nearly the whole of Africa, the " Brazilian mass " 

 and west Australia hold similar positions of areas that remained 

 relatively undisturbed. 



