Davis and Wood.] 
384 
[Nov. 20, 
smaller accomplishments, such as valleys or even canons, instead 
of with baselevelled plains. 
A conception related to the one here considered under the name 
of baselevel has been introduced by Dausse, 1 Philippson, 2 La Noe 
and Margerie. 3 When a river has deepened its channel so far as 
materially to reduce its slope and therewith its carrying power also, 
and at the same time opened extended valley walls whence it re- 
ceives an increasing load of detritus, it reaches a condition of quasi 
equilibrium, in which the further deepening of its valley is slow ; 
but deepening is only retarded and delayed, not stopped, and the 
entrance of a river into this stage of its history is by gradual transi- 
tion, not by abrupt change. While thus slowly deepening the val- 
ley, it represents in a general way the local baselevel of its region ; 
but this must not be confounded with the absolute and ultimate 
baselevel. 
The more frequent employment of the conception of baselevel 
has been accompanied by a natural evolution of its terminology. 
Powell said “base level of erosion.” Later writers omitted the 
last half of the phrase and said more briefly “base level” or “base- 
level,” the fully expanded expression being too cumbersome for 
frequent use. In this essay, we have omitted the hyphen, and 
write “baselevel” as a single word, a necessary scientific term. At 
the same time, the word has become a verb, for we often hear such 
an expression as “given time enough, and a river will baselevel its 
basin;” and an adjective, as in saying “a baselevelled region;” 
and even a noun applied to the form produced by the baselevelling 
process, as “ the upper Wisconsin baselevel,” “ the old Appala- 
chian baselevels,” meaning here the plains or peneplains of denuda- 
tion by which these districts are characterized. This is quite as 
it should be, and illustrates the practical value of the idea expressed 
in the term. 
17. Correlation of geographic development and geologic time. The 
deformation of the old Schooley peneplain has left part of its east- 
i“Profil d’dquilibre.” Etudes relatives k l’endiguement des rivifcres et aux inonda- 
tions. Mem . sav. etrangers Acad, des Sciences, xx, 1872. Here quoted from La Noe et 
Margerie, as below. 
2 “Erosioris terminant Ein Beitrag zur Erosionstheorie, Petermann’s Mittheilungen, 
1886, 67. 
3 lDtat de stability ou d’^quilibre; Les Formes du Terrain, Paris, 1888, 55, 56. Hilber 
has lately made a review of this question. Zeitschr. f. wiss. Geogr., vi, 1888, 201. 
