GEOLOGIC FORMATIONS AND SUCCESSION. 301 



2. Prairies coincident with the distribution of the medialbeds of the 

 Upper Cretaceous, occupying the outcrop of the Benton, Niobrara and 

 Taylor (Exogyra ponderosa) beds, clays and chalks, the residual soils 

 and compact calcareous subsoils of which seem ill adapted to forest 

 growth. 



3. Prairies of the Comanche series, occupying the calcareous and argil- 

 laceous terranes — all of the beds, in fact, of the Comanche series except 

 the Trinity, Paluxy and the upper Denison sands. It will be noted 

 that these beds outcrop as prairies even when they occur as isolated 

 areas in the Tertiary forested region. 



4. Prairies of the Carboniferous clays of central Indian Territory. 

 The forests are of the following kinds : 



1. The western part of the Atlantic timber belt proper, consisting 

 of (rt) pines on the post-Cretaceous gravel and sandy terranes, and (b) of 

 hardwoods — oak, ash, hickory — in the second bottoms and bottoms of 

 the streams and upper part of the Cretaceous formations. 



2. Westward-extending tongues of the great Atlantic timber belt, 

 alternating with prairies, following up the sandy alluvial riverways or, 

 on the upland, following the strike of the arenaceous terranes. The 

 latter are almost invariably oaks and elms. These upland timbers 

 follow four formations : (n) The vertical sandstone beds of the Carbon- 

 iferous, the clay beds bet^yeen being prairie, (b) The Cross Timber belts, 

 following the Cretaceous sands. They are exactly coincident with the 

 outcrop of the Trinity, upper Denison and Dakota sands to be described, 

 (c) The glauconitic sands of the uppermost Cretaceous carry hardwood 

 forests coincident with that formation, (d) The Bois d'Arc forests of the 

 Kickapoo (glauconitic marls) onl}?- occupy these beds of the Upper Cre- 

 taceous in southwestern Arkansas and northeastern Texas. 



When botanists thoroughly study the region they will see that the 

 minor flora is likewise pro])ortioned to formations, and that the structure 

 and chemical composition of the different beds in this region, aside 

 from altitudinal variation, produces the greatest differentiation of floras. 



I 



Geologic Formations and Succession. 



I have already described in previous papers, and attempted to Em- 

 phasize the importance of, the mountain system which, a little south of 

 the center of Indian Territory, extends east and west between the Can- 

 adian, the Arkansas and the Red river drainage, and also presented some 

 of its geologic features, showing that in its eastern portion at least it is 

 of typical Appalachian structure and belongs categorically to the Ap- 

 palachian geology of the United States. 



