VALLEYS OF SOLUTION IN NORTHERN ARKANSAS 



Professor G. F. Marbut has called attention to valleys of 

 solution in Missouri. 1 Before this had come to the present 

 writer's notice, he had become convinced that a type of valley 

 which occurs in large numbers in the Boone chert of Arkansas 

 owes its existence to the differential solution of the rock. 



The Boone chert lies at the base of the Missi'ssippian series 

 in Arkansas. Over a large part of the region north of the Bos- 

 ton Mountains, erosion has left this as the surface rock. It 

 approximates 400 feet in thickness and is essentially an immense 

 deposit of limestone containing chert which varies greatly in 

 amount, both horizontally and vertically. 2 



In all places where the Boone chert is the surface rock, the 

 calcareous portion has been partly removed by solution, leaving 

 a residue of chert, in places several inches deep, on the surface. 

 The universal distribution of the small chert particles over the 

 surface reduces the run-off to the minimum and increases the 

 underground water to the maximum. As a consequence, valleys 

 of solution are numerous throughout the region in which this is 

 the surface rock. So different are these valleys from those of 

 corrasion that they attract the attention of even the untrained 

 observer. While seldom of great length, their length is always 

 great in proportion to the width, and the latter is strikingly 

 uniform throughout. To borrow a term from biology, they are 

 always bilaterally symmetrical, and their slopes are steep (Fig. 

 1). They are remarkably straight, seldom deviating from a 

 straight line more than a few feet except at the points where two 

 valleys unite (Fig. 2). Probably the most striking feature 

 about them is that they head suddenly, the heads often having 

 exactly the appearance of half a sink-hole cut with a vertical 



1 Missouri Geological Survey, Vol. X, pp. 88-92. 



2 For a full description of the Boone chert, see Rep. of the Ark. Geol. Surv., 1890, 

 Vol. IV., pp. 94-107. 



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