COMPOSITE GENESIS OF THE ARKANSAS VALLEY 

 THROUGH THE OZARK HIGHLANDS 



On account of its singular course through the Ozark highland 

 region the Arkansas River presents, at the present time, unusual 

 geological interest. Its location in this part of its course, has 

 given rise to two very different opinions regarding the geologi- 

 cal age of the highlands ; and also regarding the question as to 

 whether there are two distinct uplifts, as has been advocated by 

 the Arkansas geologists, or only one, as has been urged by 

 others who have worked in the region. Recently there have 

 accumulated new data bearing directly upon the problem. 



Topographically, the Ozark highlands comprise two imposing, 

 nearly equal, elevated regions, separated from each other by a 

 broad deep trough — the Arkansas River valley. The vast plain 

 surrounding the highlands is about 400 feet above sea level on 

 the eastern side and twice this elevation on the west side. The 

 Arkansas River flows along on the horizon of this general 

 grade-plain. On the south side of the river the highlands rise 

 to heights of nearly 3000 feet above the sea; and on the north 

 to about 1800 feet. 



Diverse apparently in topographic expression, lithologic 

 composition, geologic structure, and geological age, the district 

 south of the Arkansas River has been known as the Ouachita 

 Mountains, and that north of the stream the Ozark plateau. On 

 the assumption that there are two distinct uplifts, the river of 

 Arkansas is regarded as forming a natural dividing line between 

 the two regions. At first glance, the simplest explanation for 

 the position of the stream is forced upon the attention. Pre- 

 mising a single uplift, the accounting for the waterway's course 

 meets with difficulties which, from superficial consideration, 

 appear well-nigh unsurmountable. The present note attempts 

 to sum up the evidence going to show that the facts actually 

 sustain the second premise. 



