THE CAMBRIAN GROUP OF ROCKS IN NORTH AMERICA. 



By Charles D. Waloott. 



CHAPTER I. 



INTRODUCTORY. 



This report is an unfinished memoir. It is an account of the present 

 knowledge of a great geologic group that will require prolonged inves- 

 tigation to bring it to the status in descriptive geology already attained 

 by the superjacent members of the Paleozoic system. 1 



The history of the origin and application of the term Cambrian in 

 geologic nomenclature is presented in connection with the description 

 of the names that have been employed in the classification of the various 

 formations characterized by the types of the "First or Primordial Fauna" 

 of Barrande. The basal fauna, as now kuown, is that of the Olenellus 

 zone; and the upper horizon of the group is drawn at the summit of 

 the series characterized by the Dikellocephalus fauna of North America, j 

 The delimitation of the group is based on the principles : (a) that the 

 great geologic groups must rest on the broad zoologic characters of 

 their included faunas, and not upon local stratigraphic breaks between 

 certain series of rocks or upon local differences in sedimentation; (b) 

 that the most reliable chronologic scale in geology is that afforded by 

 the relative magnitude of zoologic change ; and (c) that the geologic 

 duration and importance of any system are in strict proportion to the 

 comparative magnitude and distinctness of its collective fauna. 2 



Geologic classification has been largely based upon the imperfections 

 of the geologic record and an arbitrary assumption of breaks in the 

 chain of sedimentation and life that are not of universal extent. Geo- 

 logic continuity must have been a fact and the sequence of life and 

 deposition continued uninterrupted on some portion of the earth from 

 the earliest Cambrian time to the present day. Such continuity could 

 not have existed in any one province, and it is doubtful if the complete 

 record will ever be regained. In its absence the classification already 



1 In the preparation of the historical portion I received material assistance from Prof. Joseph F. 

 James, -who, taking as a hasis the bibliographic card-catalogne of Mr. N. H. Darton, prepared a series 

 of brief abstracts which guided me in my historical research. 



'Lap worth, Charles. Geological Magazine, new ser., dec. H, 1879, voL 6, p. 3. 



Bull. 81 2 17 



