Jan., 1908.] 
An Esker Group South of Dayton. 
2 35 
one-third its greatest width. This narrowing is produced prin¬ 
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 
which 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 Dayton appears as an oblong basin with 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. 10 That this basin and its 
tributaries do represent glacial drainage lines 17 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 would be at times of most active ice¬ 
melting, topography might to some extent be disregarded. This 
could explain the appearance of the ridges on tffe eastern side of 
the valley gap (possibly even superimposed over a continuation 
of the rock spur) rather than in the center. 18 
The close association of the eskers with kame deposits sug¬ 
gests that the latter were formed during thfe 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. Hershey, loc. cit., p. 240. 
17. F, Leverett, loc. cit., PI. II. 
18. Chamberlin & Salisbury, loc. cit., p. 375. 
