1897.] ASHLEY — GEOLOGY OF ARKANSAS. 299 



IX. Post-Carboniferous History. 

 Period from Carboniferous to Cretaceous. 



If in the sections of PI. II the strata be restored above the sur- 

 face, it will be seen that a great amount of erosion has taken place. 

 The fact that the eroded upturned edges of the Carboniferous rocks 

 have the Cretaceous rocks resting unconformably upon them is suf- 

 ficient evidence that this erosion took place between Carboniferous 

 and Cretaceous times. 



What was the extent and character of this erosion ? Mention has 

 already been made of the peculiar character of the topography along 

 the southern border of the area. Thus, if we start from the level 

 Cretaceous country and travel north over the Paleozoic, selecting a 

 road which avoids the immediate neighborhood of the larger 

 streams, as for example, the county roads to Amity from Arkadel- 

 phia, from Hollywood, from Clear creek, from Murfreesboro, the 

 Old Drove road north from Nathan, the old Stewart road from 

 Atwood toward Galena and others, we cannot help noting as we 

 leave the Cretaceous border and proceed northward that the almost 

 level character of the country continues without break, except 

 where small streams have made small valleys. The elevation 

 increases from two or three to eight or ten miles when east and 

 west valleys abruptly end the level surface. The lateral extent of 

 this flat country is governed by the encroachments of the nearest 

 streams on either side. In some cases where the tributaries of the 

 south- flowing streams run east and west the level topography 

 reaches out from the main divides and forms flat, minor east and 

 west divides, which extend almost or quite to the south-flowing 

 streams and form bluffs on those streams from 200 to 300 feet high. 

 In short, the whole topography suggests an original surface nearly 

 level, but rising gradually to the north and west over all the south- 

 ern portion of the region. Into this streams have later cut their 

 channels, in some cases to a depth of 200 to 300 feet, and in many 

 cases have eroded the surface to such an extent that all vestiges of 

 its original character are lost. The present northern boundary of 

 this flat country is exceedingly irregular, but in a general way is 

 indicated by the northward extent of the Post-Tertiary drift upon 

 the roads mentioned above, as shown on the maps. How far 

 north the Cretaceous extended is not known. A quarter of a mile 



