DEVELOPMENT OF THE INTERIOR CONTINENTAL REGION. 41 



The term Bohemian has been already used for the Upper Silurian by the 

 French geologist, M. de Lapparent, in his Treatise of 1883. The name 

 Ontarian is suggested by the actual use of the term " Ontario Division " for 

 the lower portion of the Upper Silurian by Mather, in his New York Geo- 

 logical Report of 1843, and by Emmons, in his Report of 1846. And it is 

 in its favor that Upper Silurian rocks prevail over much of Ontario, Canada. 



Cambrian, Silurian, Ontarian, would make a satisfactory triplet. What- 

 ever name shall be adopted for the Upper Silurian, the working ground of 

 Barrande, or that of Hall, Billings, and others should some way be recog- 

 nized, and to this even the distinguished author of the term Ordovician 

 would not, I am sure, enter his dissent. 



Fifthly. I come now to the " Interior Continental " region. Three sub- 

 divisions are suggested by the geology and ancient topography of the region, 

 which have eminent importance as regards rock-making. The mountain- 

 making disturbance which followed the close of the Lower Silurian left, as 

 Newberry has shown for Ohio and Western Indiana and Safford for Ten- 

 nessee, a region of shallow seas and low emergences along a belt extending 

 southwestward, parallel nearly with the Appalachian protaxial area, from 

 the west end of Lake Erie to Southern Tennessee — a region which has been 

 long called the " Cincinnati uplift." The Canadian geologists find the in- 

 fluence of the uplift extending farther north, to Lake Huron. The course 

 of this region of shallow seas and emerged land may be made the first 

 division line through the Interior Continental sea. 



The second I would draw along the western limit of the Paleozoic areas 

 on the geological map of the country, or, what is the same thing, along the 

 eastern limit of the Mesozoic, from Western Iowa southward to Texas and 

 northwestward to the Arctic coast. The Paleozoic area on the east of the 

 line was at the time, for the most part, the non-subsiding land of the conti- 

 nent. The Mesozoic area on the west of the line was the immense subsiding 

 area, for the area had the length of the continent from south to north or 

 rather northwest, and it continued its sinking through the Triassic, Jurassic, 

 and Cretaceous periods, or at least, if ceasing for part of the Triassic and 

 Jurassic, it went on through part or all of the Cretaceous period. What 

 determined this strong boundary line or limit is not clear; possibly some 

 underground Archaean feature. And perhaps uplifts at the close of Paleozoic 

 time help to mark it, if Prof. Robert T. Hill is right in referring the steep 

 upturning and flexing of the Carboniferous rocks of Western Arkansas and 

 the adjoining Indian Territory to the close of the Permian period. 



These two boundary lines divide the Interior Continental region into three 

 great sections : (1) The Eastern Interior east of the Cincinnati uplift ; (2) 

 the Central Interior or Mississippi Basin ; and (3) the Western Interior or 

 that of the Eastern Rocky Mountain slope. Of the four subdivisions laid 



VI— Bull. Geol. Soc. Am., Vol. 1, 1889. 



