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^"ORTHWARD FLOW OF CAYUGA RIVER. 358 



*'It has been a somewhat current assumption that this valley, in common with 

 the adjacent ones, is an old river trough that discharged southward through the 

 Susquehanna. If this be true, and no allowance be made, on the one hand, for drift 

 deposits in the bottom of the lake, nor, on the other, for glacial corrasion, the total 

 depth of the drift under the crest of the moraine must exceed 1,000 feet, and this 

 depth, approximately, must continue far down the Chemung-Susquehanna valley.'' 



Now that much of the depth of the lake is proved to be due to ice 

 erosion this loses some of its force, but even now the depth of drift must 

 needs be nearly 600 feet, -which of itself is almost incredible. There are, 

 however, abundant and sufficient reasons to show that the river course 

 was north and not south. In the first place, the divide itself has every 

 appearance of being a preglacial divide, modified only slightly by glacial 

 deposits. It is doubtful if these deposits reach to the height of the pre- 

 glacial divide. 



Moreover, the general plateau slope is from south to north, and this is 

 evidently a preglacial slope. Of even more importance than this is the 

 fact that in the present head-water region there is a comparatively ac- 

 cented topograph}', which, though still mature, is strikingl}^ more diver- 

 sified than that to the north. Gradually the main valley and the pre- 

 glacial tributary valleys lose in height toward the north, and near the 

 present lake outlet the valley walls retreat, on either side, as a very even, 

 gently undulating escarpment. These conditions, since they are pre- 

 glacial, seem to prove that the flow was northward, and very few^ com- 

 petent observers have doubted this. 



Since this point is of vital importance to the remainder of the argu- 

 ment, and is the one upon which most dependence is placed, I will, in 

 order that its full significance may be seen, restate it, even at the risk of 

 repetition. Cayuga valley is a preglacial valley enlarged by ice erosion. 

 Being preglacial, it shares with the other similar valleys of this plateau 

 the mature form or habit. A mature valley has a more accentuated 

 topography near its head than near its mouth. In the latter portion it 

 is broad, the valley sides are low, and the tributaries enter through val- 

 leys which, near their mouths, are shallow. As the head-waters are ap. 

 proached the valley walls become steeper, nearer together, and the 

 tributaries enter through deeper and narrower valleys than those near 

 the mouth. 



This is a fundamental principle of river development, provided there 

 has been nothing to interfere. There appear to have been no imme- 

 diate preglacial accidents in this valley, and the rock throughout its 

 leno-th is sufficientlv uniform to warrant the statement that these condi- 

 tions must be looked for in all the mature streams if they occur in one. 

 Upon the line of this argument, therefore, if we find the valley becoming 



