REPORT OF THE DIRECTOR I92O— 21 8l 



disturbances, all of which were of Precambrian time. It is further 

 to be remembered that geologists agree that these diastrophic 

 movements, especially those at the end of the Archeozoic time, 

 extended over an immense length of time; and those that involved 

 the Archean rocks were worldwide. We see then before us the 

 algebraic sum of the various diastrophic movements that successively 

 disturbed the Precambrian rocks. If then, notwithstanding these 

 facts that greatly complicate the problem of Precambrian dias- 

 trophism, we shall find that the directive lines of the Precambrian 

 diastrophic movements, as expressed in the folding and foliation of 

 all rocks and the strike of the eruptive bodies, present a striking 

 uniformity of direction over tracts of continental size, it is to be 

 inferred that these tracts responded as units for very long intervals 

 of time, if not continuously, to all diastrophic forces. 



After these preliminary discussions of the bearing of the folded 

 structures of the Precambrian rocks on the probability of their 

 indicating continental areas of the earliest recognizable surface of 

 our earth, we can turn to the evidence that is found in the literature 

 of such folds and their principal directions. 



Description of Precambrian Fold Systems 



In an attempt to trace out the primary direction of folding of 

 the Precambrian rocks it is necessary to exclude: 



1 All areas of metamorphic rocks which are either proved to be 

 or suspected of being younger than Precambrian age; such as are 

 found in Greece, Asia Minor, the Andaman and Antillean islands 

 (serpentines of Cuba, etc.), the Coast range and in Lower California, 

 New England etc. 



2 All rocks of Precambrian age involved in later folding, as those 

 of North Africa, Spain, France, western Germany, the Alps, eastern 

 Australia, etc. 1 It is to be noted here, however, that even in these 

 cases, keen observers have often enough found that the Precambrian 

 nuclei of mountain ranges retain an independent original direction of 

 folding, and further that in some cases the new folds have clearly 

 followed old lines of folding ("posthumous folds"). There are 

 further left, even in those regions that were overrun by the crustal 

 waves of later time, " islands " or blocks that remained undisturbed 

 and that give important information on the original direction of 



1 Many of these crystalline rocks have also been proved to be metamorphosed 

 rocks of Paleozoic— and some even .of Mesozoic— age. To this class belong the 

 metamorphic nuclei of the Alps, Carpathians, Betic Cordillera, Iranian arch, 

 the Himalaya, the Andes, etc. 



