8o NEW YORK STATE MUSEUM 



been demonstrated as yet, it is, however, true that wherever 

 Precambrian rocks are developed and exposed on any larger scale 

 there is a distinct succession of rocks of Archean aspect (a granite- 

 gneiss series) to more dominantly sedimentary schist series of the 

 Proterozoic era. It is not necessary to dwell on this fact at any 

 length, for it has been clearly stated in the textbooks, as Kayser's, 

 Geikie's, Lapparent's etc. In Germany one distinguishes the 

 " Urgneisformation " from the younger " Urschieferformation" ; 

 in Great Britain the fundamental gneiss (Lewisian of Hicks) from 

 rocks of Algonkian age (Pebidian). Kayser (1913, p. 34) points out, 

 that if the large unconformities observed on the Laurentian and 

 Fenno-Scandinavian shields within the Precambrian rocks and 

 between the latter and the Cambrian, have not yet been clearly 

 recognized in other regions, this is mainly due to the fact that these 

 unconformities have been entirely obscured by later folding. Never- 

 theless indications of the presence of the principal unconformity, 

 that between the Archeozoic and Proterozoic, are found in the litera- 

 ture of many Precambrian massifs in all parts of the world. 1 



There is for these reasons no doubt in our mind that the principal 

 divisions of the Precambrian are of worldwide distribution and will 

 be recognized as such as more elaborate investigation extends to 

 the as yet little known Precambrian areas of Asia, Africa, South 

 America and Australia; and especially as gradually the metamor- 

 phic rocks of Paleozoic and Mesozoic age are recognized and separated 

 from the Precambrian rocks. 



In the same way as the succession of systems elaborated in the 

 Precambrian in North America, Europe and eastern Asia will in time 

 be recognized to be as worldwide as the Paleozoic and Mesozoic sys- 

 tems are ; 2 so also the principal diastrophic events will, from present 

 indications, be found to have everywhere the same order of magnitude 

 and succession. The Archean is now everywhere known to be more 

 intensely folded, crumpled, foliated and sheared than the lower 

 Proterozoic (Agnotozoic), and this again more so than the later 

 Proterozoic. 



As several authors have pointed out, we see now in the Pre- 

 cambrian rocks the results of three revolutions and a number of 



1 The Indian Precambrian has been roughly correlated with the Canadian 

 by Sir Thomas Holland (The Archean and Purana Groups of Peninsular India; 

 Compt. Rend. 12 Intern. Geol. Congr. 1913, p. 370 ff.) and an unconformity 

 pointed out in the Archean corresponding to that separating the Laurentian 

 and Huronian and another one separating the Archean and Purana groups, 

 which latter (consisting of the Gwalior and Vindyan) is correlated with the 

 Algonkian. 



2 It is, for example, recognized in Brazil by Harder and Chamberlin (1915). 



