220 



The investigation of the ridge, which was undertaken under the direc- 

 tion of the Arkansas geological survey, revealed its general geological 

 structure to be about as follows : The top of the ridge is, in portions of its 

 extent, capped with pleistocene deposits of relatively both early and late 

 epochs. The newest deposit of value is the loess which caps or lines the 

 highest portions of the ridge ; this material shows a bi-partite character 

 which is believed to be connected with at least two glacial epochs the 

 facts concerning which have been collated and discussed by Messrs. 

 Chamberlain and Salisbury in several papers in the geological journals. 

 Below this material, where it crowns the ridge, is a heavy deposit of a 

 cherty gravel, much ferruginized, water-worn, not well assorted, and of 

 varying thickness. This is elsewhere shown to be of tertiary age. Be- 

 low this member is a great thickness of tertiary sands, usually non-in- 

 durated and soft, yielding readily to erosive action. The lowest member 

 disclosed to the observer is made up of alternating pure and sandy clays, 

 with much lignite in masses or disposed in great beds often many feet in 

 thickness. Towards the base of the exposed clays many localities have 

 yielded large numbers of fossil leaves which determine the age of, the 

 clays as early eocene. Added to their evidence is that furnished by the 

 rather rare localities where fossil shells have been found. These are all 

 marine and are unequivocally eocene. At numerous localities in the 

 northern half of the ridge the gravel member alone forms the highest 

 points of the hills the loess, if it ever existed there, having been en- 

 tirely eroded away. The gravels often have small masses of a very com- 

 pact and fine grained quartzite and much rarer large masses often weigh- 

 ing several hundred pounds. These increase in frequency along the west 

 side of the ridge until near the Missouri line, some twenty-five miles 

 south of it, where they no longer appear. They are usually quite white 

 in color but in the gravels the smaller ones seem to have acquired the 

 characteristic ferruginization of the gravels of the orange sand. 



It happened that one of the problems connected with these nodular or 

 pebbly quartzites related to their origin. They presented nothing in com- 

 mon with such quartzites as are familiar to all students of the northern 

 drift and were to be in no way connected therewith. It was noticed that 

 they became more and more abundant as progress was made towards the 

 northern portions of the ridge, but this fact only added another phase to the 

 riddle to be solved. Dr. D. D. Owen, whose geological work needs no in- 

 troduction or word of commendation to an Indiana scientist, had years 



