STRATIGRAPHIC TAXONOMY 611 



Silurian, Devonian, Waverlyan, and Tennessean; the Mesozoic, including 

 the Penns3'lvanian, Jiira-Triassic or Newarkian, Comanchean, and Cre- 

 taceous. The proposed downward extension of the Mesozoic so that it 

 will begin with the Pennsylvanian will probably aronse more opposition 

 than the reduction of the Permian, the Triassic, and the Jurassic to the 

 rank of series. But a strict and entirely consistent application of the 

 principles of correlation by diastrophic movements demanded nothing 

 less. If, in following their lead, I have fallen into error, it is either be- 

 cause the principles are at fault — which I am loath to believe — or be- 

 cause the available data have been misinterpreted. With my present in- 

 formation these, as well as all the other proposed changes, are confidently 

 believed to tend toward the coordination of the major divisions of the 

 geologic time scale. And this feature is deemed a prime desideratum, 

 if, indeed, it is not a requisite, in the construction of a permanent classi- 

 fication. 



EoPALEozoic Formations 



CAMBRIAN SYSTEM OR PERIOD 



Definition of the term Cambrian. — It is not my intention to enter 

 into an extended discussion of the varying uses of this term. Beyond 

 making it clear which part of the stratigraphic column I am referring 

 to when the word Cambrian is used, it will suffice to say that as proposed 

 and commonly used by Sedgwick, the author of the term, it corresponded 

 practically to the Eopaleozoic of Dana and the present work, and of the 

 Eopaleozoic, and, in other parts of his recent work, of the restricted 

 Paleozoic, of Schuchert. Following the indefinite separation of an upper 

 part of the Eopaleozoic by Lapworth under the name Ordovician, an 

 innovation that has been generally adopted in America where it dis- 

 placed the previously used "Lower Silurian," the Cambrian was cor- 

 respondingly restricted. But a definite boundary between the Cambrian 

 and the Ordovician was never satisfactorily established. Some drew the 

 lower limit of the Ordovician at the base of the Saint Peter sandstone, 

 others thought it should be drawn somewhere between the middle and 

 base of the Canadian, while others again limited the Cambrian to deposits 

 beneath some undetermined and variously correlated middle or lower 

 Ozarkian zone. 



As here used, the term Cambrian refers to strata beginning with the 

 basal part of the oldest formation containing the "Olenellus fauna" or 

 trilobites belonging to the family Mesonacidce. The upper boundary is 

 drawn at the apparently universally recognizable hiatus, which marks the 



