COMMUNICATION 



To the Editor: 



The comparison of shapes of valleys to capital letters of the alphabet 

 — U for glaciated valleys and V for those due to ordinary river erosion 

 has long been used quite helpfully in textbooks of physiography, I 

 have found a few other letters of the alphabet helpful in the same con- 

 nection. I submit them to you and to other teachers for suggestion 

 and criticism: 



l-shaped valleys — extremely young, of the canon type, corrasion 

 very rapid with relation to lateral weathering; 



V-shaped valleys due to river erosion, width of V dependent on the 

 ratio of weathering to corrosion; 



Y-shaped valleys — rejuvenated, the grade of the river has been 

 recently increased by uplift or up til ting of the head waters; 



W-shaped valleys — the river acting as a distributary in a flood 

 plain which is highest near the river, grade of the river therefor decreasing 

 either by uptilting of the mouth or down tilting of the head waters, or 

 otherwise. The application of the letter W to this form of valley is 

 something of a stretch, yet I find it well worth while to emphasize the 

 fact that such streams as the Mississippi and the Poe have as the highest 

 part of the flood plain that immediately near the river, so that a cross- 

 section of their valleys has more the shape of a cross-section of a plate 

 or pan. In fact I have used the term pan-shaped for these sections. 

 But it is schematically desirable to use another letter, and W lends 

 itself fairly well. U-shaped valleys remain as usual glaciated valleys. 



Alfred C. Lane 



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