XXVI 



PREFACE. 



structural changes in the Archean are seldom abrupt and evident, and that even 

 from one rock species to another there are usually intermediate transitions which 

 sometimes baffle reasonable interpretation. This scheme, therefore, must be under- 

 stood to present only the broader features of the rock succession. 



NOD < "NKOK.MITY. 



The reader will find in Part I a description of these formations, and in Part III 

 a discussion of their genetic relations. 



The term Norian is replaced by Cabotian because of its original application to 

 a Mesozoic formation of the Alps, as shown by Renevier.* 



ROCKS LEFT AT PARIS. 



In order that European geologists may examine the rocks discussed in this 

 volume, and thus be enabled to review the petrographic conclusions, a series of 118 



* Ambiguite du term Norien, et son inadmissibilite dans la classiflcation Internationale. Eclogae ge.ologicae, vol. 5, p. SSS. 



