648 E. O. ULRICH EEVISIOX OF THE PALEOZOIC SYSTEMS 



marily by virtue of the ^^principle of maximum thickness of overlapping 

 formations" (see page 554). Corroborative evidence, however, is found 

 in north Arkansas and Missouri, where the Jefferson City dolomite is 

 succeeded unconformably by Canadian beds containing a fauna that is 

 found in Oklahoma nearly 4,000 feet beneath the top of the Arbuckle 

 limestone — that is, beneath the base of the Ordovician, which begins here 

 with the Simpson formation. The fauna! evidence points to the same 

 conclusion, the Jefferson City fossils, so far as they go, being clearly 

 Ozarkian, while the Stonehenge-Tribes Hill fauna is as clearly Canadian^ 

 and not Ozarkian. I wish it to be understood, however, that in my 

 opinion the upper Ozarkian formations in Missouri do not completely 

 fill the gap between the top of the Gasconade zone in the Little Falls 

 and the base of the Tribes Hill-Stonehenge overlap. There is a fair 

 chance that certain deposits in the Atlantic province may finally be 

 added to the base of the Canadian. 



Eegarding, also, the upper boundary of the Canadian, the bare possi- 

 bility is recognized that the "Saint Peter series" may be in part the 

 equivalent of the basal portion of the heavily developed Stones River 

 group in the Appalachian Valley. But the Saint Peter is found in deep 

 wells in central Kentucky beneath the Stones River. Besides, in Mary- 

 land and Pennsylvania, as frequently noted in this work, an uncon- 

 formity separates the thickest Stones River from the youngest of the 

 Canadian formations recognized in the Appalachian Valley. The Day 

 Point Chazy likewise lies unconformably on the highest Beekmantown. 

 It is altogether reasonable, therefore, that the Saint Peter belongs in 

 this gap, though it probably does not fill it. 



Authority for the name. — As originally defined by Dana in 187/^ 

 and as employed since by himself and other authors, the term Canadian 

 was applied to the middle one of three divisions of the Lower Silurian. 

 Beneath the Canadian, which included the Quebec group of Canada and 

 the Calciferous and Chazy of 'New York, came the Primordial period; 

 above it the Trenton period. The inclusion of the Chazy doubtless was 

 induced by the supposed mixture of Calciferous and Chazy faunas in the 

 Quebec. Indeed, as determined by Logan and Billings, the Levis grapto- 

 lite fauna seems to occur in w^estern Newfoundland above faunas that, 

 but for this, would have passed very well for Chazy or even younger Ordo- 

 vician. The Chazy fauna, too, had always been set apart from those of 

 the "Trenton periods'' as quite distinct and presumably older. Under 

 the circumstances the Chazy could not be logically separated from a group 



