

across Mississippi, Louisiana, and Texas. 359 



extension of some small south-flowing stream has been taken 

 into consideration, but such an hypothesis claims little atten- 

 tion in this case. The lower Mississippi since Cretaceous times 

 must be either the direct descendant of Carboniferous drainage, 

 or else it has been produced by a depression in the lower Mis- 

 sissippi area which also caused a reversal of the Arkansas Val- 

 ley drainage. Let us first consider the reasons for believing 

 the drainage of the Arkansas reversed. 



On any emerging coast the streams flow from the older 

 toward the newer beds. Along the Atlantic slope the streams 

 flow from the Paleozoic uplands across Triassic, Cretaceous, 

 Tertiary, Pleistocene and recent deposits into an ocean where 

 sediments are actually being laid down. In the same way the 

 emerging Carboniferous lands must have had their drainage 

 flowing from new Carboniferous beds into Permian seas, and 

 later, as emergence proceeded, these streams must have flowed 

 across Permian sediments into Triassic waters, and so on, as 

 long as the orographic movements were even. Now in 

 Arkansas the succession of the beds, in the order of their depo- 

 sition from the Carboniferous upwards, is found by going west- 

 ward up the Arkansas and Canadian rivers into Indian Territory 

 and Oklahoma. Along such a section one passes from the 

 Lower to the Upper Coal Measures, thence to the Permian, 

 Triassic, Cretaceous, and Tertiary in their order ; and this 

 must have been the direction of the drainage while these beds 

 were being deposited. That is, the sea that occasionally 

 invaded this region receded westward and was gradually 

 crowded in between the Ozarks and the Kocky Mountains. 

 Further, the area between the Ozarks and the Ouachita uplift 

 is structurally a great synclinal trough dipping westward. 

 These structural features must have determined the direction 

 of the drainage during Carboniferous and later times. The 

 Arkansas river therefore flows, not with the dip of the rocks, 

 as it did originally, but against it. Such a state of affairs 

 would be brought about by the lowering of the Mississippi 

 River region. The amount of depression necessary to reverse 

 the drainage is given on p. 360, under the head of the " Slope of 

 the Ouachita uplift." 



Although Cretaceous and Tertiary beds fill the Mississippi 

 embayment, there are neither Permian, Triassic nor Jurassic 

 rocks exposed anywhere beneath them or along their edges. 

 Whatever may have happened in the lower Mississippi area, 

 it is therefore reasonable to suppose that the drainage flowed 

 westward through the Arkansas Valley during Carboniferous, 

 Triassic and Jurassic times, and entered the Mediterranean sea 

 that lay along the eastern base of the Pocky Mountains. And 

 the reason for this westward Carboniferous and later drainage 



Am. Jour. Sci.— Fourth Series, Yol. IV, No. 23.— Nov., 1897. 

 25 



