354 The Ohio Xaturaiist. [Vol. VIII, No. 7, 



sions, the following conclusions may be reached. During pre- 

 glacial time a system of valleys was here developed — valleys 

 which had reached maturity. This maturity was more marked 

 in and near the master valleys but became less and less strong 

 as one pushed back up the little valleys. Many of the latter, 

 especiallv south of the large east and west valley, gradually 

 widened northward showing that the line of headwater divides 

 must have lain near but south of this large valley. 



The advancing ice would move more easily into the broad, 

 mature valleys and into those lying more nearly in the direction 

 of ice movement. The ice pushed in from the north, as it came 

 into rougher and rougher topography it broke up into tongue- 

 like dependencies,* which extended into the valleys. While 

 the ends of the tongues were fairly stationary, melting freed 

 rock waste which accumulated in moraines. Any stream flow- 

 ing toward the advancing ice would of necessity find its course 

 closed during the ice advance by ice and moraine. The water, 

 augmented by the melting of the ice, would accumulate in a 

 lake between the advancing ice on the north, the valley walls 

 on the sides and the divides on the south. Its outlet would be 

 over the lowest places, whether of moraine or rock, whether in 

 valleys or over low cols between ridges at the very heads of the 

 streams. Thus was begun the discharge of water over the 

 divides. As the ice continued to advance it crossed one of the 

 divides and may have lowered it some by ice erosion, but this 

 if done, is not ver}^ apparent. 



While the ice front lay along the large east and west valley 

 studied, it built masses of moraine in the valley and water rose 

 in the tributary valley leading southward from Loudonville 

 until it was pushed over the divide at Spellacy. When the ice 

 withdrew, it became more markedly a series of valley depend- 

 encies, and the water accumulated in front of their noses until it 

 went over the col in Muddy Fork northwest of Lakeville, but 

 because of ice obstructions it could not go along the large valley 

 leading to Big Prairie. Thus was started the stream over the 

 divides between the narrow valleys and not along the earlier 

 mature valleys. 



Once started it was easier for the stream, when the ice with- 

 drew, to maintain its course over the divides than to seek its 

 old routes. Hence the cutting down continued and the little 

 narrows were finally cut to present dimensions. The cutting 

 down of the divide gave all side streams near the divide a chance 

 to deepen their courses near their mouths which the}^ proceeded 



*Camey, F. (Jour. Geol. XV, 1907 pp. 4SS ff.) very happily applies 

 this term to peripheral protuberances, which extended frona the great 

 ice sheet into preglacial rock valle3^s. 



