Jan., 1908.] A?i Esker Group South of Dayton. 235 



one-third its greatest width. This narrowing is produced j;rin- 

 cipally from the eastern side by a rock spur (Fig. 1), south of 

 which the valley again widens but not to its former size. The 

 last rock outcrop on this spur was found on its top and several 

 hundred yards from the end. The Bluffs extend west-southwest 

 from this spur, the two prominences being separated by a gap 

 wdiich permits the egress of drainage from a small valley (S. V., 

 Fig. 1) connected with the spur. The eskers and kame area 

 spreading southward from the Bluffs cut off a small segment of 

 the Great Miami Valley (V. S., Fig. 1) lying south of the spur. 



Theories of Origin. In diagrammatic view (Fig. 1) the valley 

 of Davton appears as an oblong basin w^ith wide gaps for the en- 

 trance of the Miami River and tributaries, and one for the de- 

 parture of the combined drainage. This great basin may have 

 exerted an important influence on the waning glacial ice in con- 

 trolling its movement in this area, and also in concentrating 

 drainage that became sub-glacial. ^'^ That this basin and its 

 tributaries do represent glacial drainage lines^^ is proved by the 

 great depth and character of the debris filling. The over-riding 

 ice would drop into the Dayton valley as in a pocket. This in 

 the stagnant ice stages would accentuate its immobility thereby 

 conducing to esker-forming conditions. The concentrated drain- 

 age would seek the point of easiest egress which would probably 

 be somewhere in the gap to the south. While under great head, 

 as doubtless the drainage w^ould be at times of most active ice- 

 melting, topography might to some extent be disregarded. This 

 could explain the appearance of the ridges on the eastern side of 

 the valley gap (possibly even superimposed over a continuation 

 of the rock spur) rather than in the center. ^^ 



The close association of the eskers with kame deposits sug- 

 gests that the latter were formed during the retreat of the ice 

 after the eskers had been built in sub-glacial stream tunnels. 

 This kame area doubtless spread originally further across the 

 valley but has in part been removed by the meanderings of the 

 Miami River. The abrupt face presented to the north by the 

 Bluffs may also have the same explanation; it has already been 

 noted that this river flows at the present time along their base. 

 If this explanation is correct, the kame and esker topography 

 may formerly have extended an indefinite distance northward 

 into the Dayton Valley. 



Detailed Description of Eskers. It is unsafe to number these 

 ridges as marking separate and distinct lines of drainage, but for 

 convenience this method will be adopted. The easternmost will. 



16. I. C. Russell, Jour, of Geol.. Vol. Ill, (1895), p. 827. 

 O. H. Hershev, loc. cit., p. 240. 



17. F, Leverett, loc. cit., PI. II. 



18. Chamberlin & Salisbury, loc. cit., p. 375. 



