76 I. C. RUSSELL — HANGING VALLEYS 



end of a tributary valley is distinctly above the level of its main the 

 former is called a " hanging valley."* 



The first of these definitions restricts the term defined to the valleys 

 of formerly glaciated regions, and ascribes to them a single mode of 

 origin. As I hope to show in the following pages, a discordance in 

 gradient between a main valley and its tributaries is not strictly con- 

 fined to glaciated regions, and may result from one of several processes. 

 For my present purpose, therefore, it is necessary to give a more com- 

 prehensive meaning to the term hanging valley than is done in the first 

 definition referred to. The second definition is more general than the 

 one framed by Gilbert, and does not imply mode of origin, but can per- 

 haps be amplified in order to make it more graphic. 



Provisionally and as used in this paper the generic term hanging 

 valley maybe understood to include any valley or valley-like depression 

 the bottom of which is not in even adjustment with the bottom of the 

 lower depression with which it unites and into which it drains, the 

 passage from one to the other being by means of a slope of greater 

 declivity than the gradient of the tributary valley, and in most instances 

 precipitous — that is, hanging valleys are in striking contrast to the con- 

 ditions normal to mature steam-eroded valley systems, in which, as was 

 long since pointed out by Playfair, the branches of the system at their 

 mouths are nicely adjusted to the level of the lower valley with which 

 they unite. 



The definition just presented takes account of present topographic 

 conditions only, without reference to the manner in which the discord- 

 ance in gradients referred to came about. 



In attempting to define "species " under the hanging valley "genus " 

 mode of origin may be taken as the leading criteria, and more or less 

 conspicuous differences in hanging valleys produced by the same agency 

 suggest the recognition of " varieties." 



Classification 

 en umera tion of species 

 Our present knowledge of hanging valleys seems to warrant their pro- 



*The nature and mode of origin of hanging valleys has been discussed by W. M. Davis in an 

 article entitled "Glacial erosion in France, Switzerland, and Norway," in Boston Society of Nat- 

 ural History Proceedings, vol. 29, 1900, pp. 273-321. To the bibliography presented in this paper 

 the following titles of subsequent publications treating of hanging valleys may be added : 



W. O. Crosby : " The hanging valleys of Georgetown, Colorado." Technology Quarterly, vol. 

 xvi, 1903, pp. 41-50. 



Ralph S. Tarr: "Hanging valleys in the Finger Lake region of central New York." American 

 Geologist, vol. xxxiii, 1904, pp. 271-291. 



