STRATIGRAPHIC TAXONOMY 647 



the Ozarkian. Possibly these flags, together with the overlying Tre- 

 madoc — represented on the American side by the Bretonian in Xew 

 Brunswick — are intermediate in age between the top of the Ozarkian in 

 Missouri (Jefferson City dolomite) and the base of the Canadian at 

 Belief onte, Pennsylvania ; but for the present I prefer to regard them as 

 Atlantic deposits, corresponding in a general way to the lower divisions 

 of the Canadian as now recognized in America. They may be in part a 

 little older than the Stonehenge and Tribes Hill limestones, but the 

 higher parts probably are younger. The principle of rhythm in dias- 

 trophic movements alone seems to hold out any definite promise of a 

 final disposition of these difficult Atlantic deposits in the geologic 

 time scale. (See discussion of the Dictyonema zone, page 678.) 



In the Swedish and Kussian Baltic sections the Ozarkian is almost 

 certainly absent. So far as known, then, the Ozarkian seems to be 

 confined to North American areas. Schuchert's alternative use of Cam- 

 brian for Ozarkian, therefore, is as yet groundless. 



CAXADIAX PERIOD OR SYSTEM 



Definition of the term. — To the Canadian system I refer all deposits 

 that on the one side can be shown, or which are believed, to be younger 

 than the last of the Jefferson City dolomite in Missouri and the 

 Shakopee in the upper Mississippi Valley, and which on the other side 

 are thought to be older than the first sandstone and limestone (Everton) 

 of the Saint Peter series in northern Arkansas. In other words, the 

 Canadian embraces the wide interval that began with the first advance 

 of the sea following the closing withdrawal of the Ozarkian seas, and 

 which ended with the last emergence preceding the first or Saint Peter 

 advance of the Ordovician waters. 



The truth of the belief that the Stonehenge limestone, which lies at 

 the base of the Canadian in Pennsylvania, is younger than the highest 

 of the formations in the Mississippi Valley referred to the Ozarkian is^ 

 positively demonstrable, on the basis of superposition and horizontal 

 continuity of sediments and faunas, only to the top of the Chepultepec 

 or Gasconade faunal zone. However, as this zone is succeeded uncon- 

 formably in the Mohawk Valley by the Tribes Hill limestone, which con- 

 tains characteristic Stonehenge fossils, the remaining upper Ozarkian 

 (Eoubidoux- Jefferson City) part of the stratigraphic sequence is in- 

 serted by inference in the hiatus between the base of the Tribes Hill 

 and the Gasconade zone at the top of the Little Falls. This is done pri- 



