REPORT OF THE DIRECTOR I920-2I 115 



We have seen in the chapter on the Precambrian fold systems of 

 Eurasia, how the later folds of the Urals and the Timan, in a large 

 part, coincide with the Precambrian folding of the region, which 

 is a western continuation of the Sayan system of the Angara shield; 

 and it is also noteworthy that the Predevonian Caledonian folding, 

 which according to Suess (v. 3, pt 2) is intercalated between sup- 

 posedly Laurentian remnants and the western portion of the Asiatic 

 structure, follows in general the trend lines of eastern Laurentia. 

 Likewise, the metamorphic rocks of Tonking and Cochinchina, 

 together with younger rocks, strike like the original Precambrian 

 basement complex of eastern Asia, that is, toward northeast, the 

 metamorphic rocks of Formosa to north-northeast and those of 

 Japan to east-northeast; thus all remaining in the same quadrant 

 with the Precambrian folding. 



It may therefore be stated as a general proposition that apparently 

 a great portion of the Paleozoic folds do not diverge greatly in their 

 directions from the preceding Precambrian trend lines and thus have 

 remained, to a large extent, under the influence of the original 

 trend lines inherited from Precambrian time. 



It is readily seen that the evidence of the posthumous folds is 

 largely corroborative of the conclusions drawn in regard to the 

 existence of large entities of Precambrian fold and foliation systems, 

 in so far as it shows the marginal regions of these large entities 

 invaded by folds that run approximately parallel to the original 

 Precambrian fold directions. 



In summing up the conclusions from the Precambrian and post- 

 humous Paleozoic folds we have reached thus far the following 

 propositions : 



The Precambrian fold and foliation systems prove that there 

 existed in Precambrian time several large crustal segments that 

 reacted as entities against the universal Precambrian folding of the 

 crust of the earth. These entities comprise as far as known, Eur- 

 asia, North America-Greenland, Africa-Madagascar-East India- West 

 Australia. Certain nuclear or central parts of these large entities 

 became early so intensely folded, that they became " stiffened " 

 blocks (Suess & Stille, 1909) and have been avoided by all younger 

 folds. The most noted of these " shields " are the Angara shield 

 in Asia, the Baltic shield in Europe and the Laurentian shield in 

 North America. The greater part of Africa represents a similar 

 shield that has remained free from younger folding and acted as 

 a folded older block in the north and south against younger folding. 



We have further seen that where these large entities were affected 



