228 ASHLEY — GEOLOGY OF ARKANSAS. [May 13, 



mountain. This, then, became the centre of drainage for south- 

 western Arkansas and the adjacent part of the Indian Territory, 

 the streams flowing away in every direction over the newly exposed 

 beds of Cretaceous material. A glance at a map of Arkansas and 

 Indian Territory will show that the streams thus started have per- 

 sisted to the present. 



After these streams had cut through the overlying Cretaceous 

 they struck the hard layers of Carboniferous sandstone, and slowly 

 cut their channels down through the harder layers standing across 

 their path. In the course of time the Cretaceous beds were com- 

 pletely removed from the region north of the existing Cretaceous 

 border. The period ends with the deposit of Tertiary beds over 

 the eastern end.^ 



A Recent Subsidence. — There has been a recent subsidence of the 

 region which probably did not submerge the novaculite mountains 

 to the north, but brought them in range of wave action. The hard 

 novaculites tend to disintegrate into blocks rather than fine material, 

 and as the waters receded, these blocks of novaculite with others of 

 sandstone were rounded by wave action, broken up and the whole 

 scattered as a great gravel bed, in places at least one hundred and 

 fifty feet deep and probably much more, over the area and far to 

 the south. This subsidence is thought to have taken place in post- 

 Tertiary time. The greater portion of the novaculite and sand- 

 stone drift laid down in the preceding period has been removed re- 

 cently, leaving only a narrow strip undisturbed on the southern edge, 

 and in patches all over the region, where the larger boulders have 

 resisted erosion. 



III. Original Stratigraphy. 



In this chapter will be considered the character, thickness and 

 manner of deposition of the Paleozoic beds. It will be practically 

 a consideration of the first period in the history of the region, as 

 outlined in the preceding chapter. 



Petrology. 

 Rocks of the Novaculite Series.'^ — The divisions of the rocks of 

 the novaculite series made by Mr. Griswold will be followed. 

 These rocks he divides as follows : 



1 Geol. Surv. of Ark., An. Rep. for 1892, Vol, ii. 



2 Geol. Szirv. of Ark., An. Rep. for 1890, Vol. iii, p 



