d^d FRANK S. MILLS 



aggraded by the fluvio-glacial debris. Later, the extra-morainic 

 wash from the highly developed "kettle" morain, or the terminal 

 morain of the second ice advance, lying only a few miles to the 

 north, must have overwhelmed these intrenched valleys with 

 floods of drift, under which their floors now lie deeply buried. 



The proximity of the halted ice-front, and the immense load 

 of detritus carried on, in, and beneath the ice, must have 

 aggraded with tremendous rapidity the narrow valleys adjacent 

 to it. The volume of drainage, fed by subglacial streams, by 

 the general melting of the ice-front, by drainage from the land 

 just released from the ice, and by the presumed greater precipi- 

 tation of the glacial epoch, must have filled these valleys with 

 streams of great volume, even after the continuity of the ice- 

 sheet was broken by the melting upon hilltops and divides. 

 Under such conditions it is not credible that the stream can be 

 classed as one of either constant volume or load. 



Drainage to the north was held in restraint by the blockage of 

 the ice-front itself, and such conditions must have existed in 

 north-sloping valleys as to transform them into temporarily 

 ponded basins. The north-sloping valleys having become regions 

 of more or less static water, the lower part (preglacially) of these 

 valleys would be the points of greatest deposition. Helped in 

 great measure by such aggrading and filling, the northward 

 streams were compelled to flow over their former divides and 

 adopt a southward outlet. 



With the steady retreat of the ice two conditions of para- 

 mount importance must have been imposed upon the drainage: 

 diminution in load, and a gradually diminishing volume. Both 

 of these factors are of importance in the solution of these ter- 

 races, for a differential of either would affect the activity and 

 scope of stream excavation. In the case in hand bold spurs do 

 project into the valley flanked by terrace plains, but the inter- 

 esting fact in regard to them is that the terraces appear on the 

 north side, or up-valley, of the projecting spur, while the drain- 

 age flows to the south. It has been shown by Davis, both in 

 text and by a variety of progressive illustrations, that terraces 

 related to protecting spurs are removed by the stream on the up- 



