Ill 



lu the Boone chert region of northern Arkansas, there are many 

 alluvial cones, composed almost entirely of fragmentary chert. This 

 chert withstands weathering to a remarkaljle degree. It readily permits 

 the rainfall to pass through it, thus preveuting erosion, and forming an 

 ideal protection for the underlyiug rocks. 



Ali-o, over this region, there are numerous knobs of the character 

 shown in Fig. 6. These knobs are capped with fragmentary chert, resting 

 upon the magnesian limestone that underlies the Boone chert. The sur- 



F.S.6 



rounding geography is thai sliown in Fig. 4. Nearly all the capping 

 material is angular, lint close search will often reveal water-worn pebbles. 



The writer is of the opinion that the capping material is that of 

 alluvial cones, and that the preservation of the rock beneath from erosion, 

 is due to the protection afforded l)y the cones. Such knobs are sometimes 

 500 feet above the valley-; lieneath. The small number of water-worn 

 pebbles is accounted for in the fact that the debris of the cones was 

 transported Imt short distances, and there was not time for much round- 

 ing. Besides, the material is hard, and would Avear slowly. 



The material of these old cones must not be confounded with the 

 gravel that is common in this region, and which occurs on the hill sides 

 (see Fig. 6) often extending up to the height of 200 feet or more above 

 the present stream level. This material, imlike that capping the knobs, 

 is all water-worn, and was left on the inside curve of the streams as they 

 shifted laterally. 



