181)7.] ASHLEY — GEOLOGY OF ARKANSAS. 227 



SO that, with the scarcity of outcrops, it is impossible to follow or 

 trace the anticlines with accuracy, though in many cases, by means 

 of their effect upon the topography, they may be followed with 

 some degree of accuracy for long distances. 



These folds have a nearly east and west trend, and are crossed in 

 traversing the region in a north and south line. 



On one such line there are as many as thirty-nine anticlines in a 

 distance of twenty-four miles. Many of these anticlines cannot 

 be found at more than one place, others may be traced for a score 

 or two of miles. Normal anticlines sometimes merge into over- 

 turns. 



A Period of Erosion and Sinking. — As already suggested, the ero- 

 sion during the period of active folding may have been consider- 

 able ; so that it is probable that at no time did the elevations over 

 the area at all approach the altitude that a restoration of the 

 eroded strata would make. At last the time came when erosion 

 exceeded elevation and probably sinking took place over the whole 

 region. This resulted in the formation of a base level of erosion.^ 

 That is, the land level in its lowest part was so near sea level that 

 subaerial erosion was entirely expended in wearing down the eleva- 

 tions, and as the sinking proceeded and the oceanic waters ad- 

 vanced, wave action completed the leveling process. Evidences of 

 this old sea bottom are abundant; only the narrow remnant of flat 

 country fringing the south edge of the area need be mentioned here. 



The exact extent of this inundation is unknown, but there are 

 reasons for believing that it extended north of the region under con- 

 sideration.- During this inundation the Cretaceous beds, of which 

 a remnant is still found lying unconformably on the southern edge 

 of the region, were laid down. 



All details of the record of events during Cretaceous times are 

 lost in the region to be studied, the evidence only permitting us to 

 say, that some time previous to the Cretaceous the area was re- 

 duced to a base level, after which the Cretaceous beds were laid 

 down. The region may have subsequently been subjected to 

 several periods of erosion and deposition. 



Following some or all of these periods of deposition came eleva- 

 tion, with the centre of elevation in the neighborhood of the Rich 



1 Button, Te7-iiary History of the Grand Cation District, p. 76. 

 '' Geol. Siirv. of Ark., An. Rep. for 1890, Vol. iii, p. 220. 



