494 JOHN LYON RICH 



Effects of a tilting uplift. — In the above analysis we have con- 

 sidered the drainage system as being uphfted bodily — the mouth 

 of the stream as much as its headwaters. We were led to the con- 

 clusion that under those conditions the type of valley in the upper 

 course of a stream would normally be different from that in the 

 lower course. 



If the uplift were of a tilting nature with the axis at the mouth 

 of the master stream and with the headwaters receiving the greatest 

 uphft, the upper reaches of the stream would feel the effects of 

 the uplift as soon as any other part of its course, and, if the uplift 

 were rapid, it would seem that the type of valley associated with 

 rapid uplift would prevail throughout. 



If we may safely reason from the deductions outlined above, 

 we may conclude that, where rock textures do not complicate 

 matters too much, a drainage system with valleys of the type 

 representing rapid uplift in its lower part, and with types repre- 

 senting slow uplift in its upper branches indicates, though, on 

 account of other complicating factors, it may not prove, a rapid 

 bodily uplift of both headwaters and lower course, while one dis- 

 playing the forms associated with rapid uphft throughout its course 

 indicates a rapid tilting uplift, with maximum elevation in the 

 upper parts of the drainage system. Effects of tilting in the oppo- 

 site direction need not be considered here : the reader may readily 

 work them out for himself. 



If this criterion of tilting is found to hold good it might be 

 possible, in the case of a fairly extensive dendritic drainage system, 

 to determine the axis of tilting by noting the types of valleys in 

 streams coming in from different directions and therefore affected 

 differently by the tilting. 



SPECIFIC APPLICATION OF THE CRITERIA. 



As an example of the application of the criteria outlined in 

 preceding paragraphs we may take the case of the Mississippi 

 River as illustrated on the Waukon (Iowa- Wis.) sheet. The river 

 here is flowing in a flat-bottomed valley of the open type some 

 two miles wide and with steep, smoothly trimmed and parallel 



