176 



SCIENCE. 



[N. S. Vol. I. No. 7. 



Geology, II., 1894, 33.) Further on in the 

 same article, he writes of the ' deformation 

 of the baselevel.' Although the writer has 

 repeatedly made a similar use of the term, 

 it now seems doubtful if it should be used 

 so freely ; and some such word as peneplain 

 might serve to replace this extension of the 

 original meaning of baselevel. This is the 

 more advisable, when it is considered how 

 very seldom a region is reduced sensibly to 

 baselevel; how generally a long eroded 

 surface still retains some faint inequality of 

 form which should be expressed in its name. 



GEOMOBPHOLOGY OF THE SOUTHERN APPA- 

 LACHIANS. 



The interpretation of the development of 

 geogi'aphical features in accordance with 

 the general theory of baselevelling has re- 

 ceived two notable contributions during the 

 past year. The first is by Hayes and Camp- 

 bell on the Geomorphology of the Southern 

 Appalachians ( N"at. Geogr. Magazine, VI., 

 1894, 63). The authors recognize the wide- 

 spread occurrence of more or less fully de- 

 nuded peneplains at two levels, one of late 

 Cretaceous, the other of late Tertiary date, 

 thus extending the conclusions reached by 

 others farther to the north. They then 

 proceed to measure the amount of deform- 

 ation that the peneplains have suffered by 

 drawing contour lines upon them. It ap- 

 pears very clearly that the axes of elevation 

 along which these old lowlands have been 

 arched up, coincide closely with the Appa- 

 lachian axis; thus adding two more dates 

 to the many others at which this Une has 

 been the scene of deformation. The tilting 

 of the surface of the deformed peneplains is 

 regarded as of importance in determining 

 the capture and diversion of certain streams 

 by their rivals; this principle being further 

 illustrated by Campbell in a separate article 

 on ' Tertiary changes in the drainage of 

 southwestern Virginia' (Amer. Journ. 

 Science, XLVIII., 1894, 21). 



GKADED RIVERS. 



A RIVER that ceased the active deepening 

 of its valley is by various ■^Titers described 

 as havmg reached its baselevel. Thus A. 

 Winslow writes : " The streams of the prai- 

 rie country have, in large part, 



reached base level, ani are developing me- 

 ander plains." (Missouri Geol. Survey, 

 VI., 1894, Lead and Zink deposits, 310.) 

 H. Gannett figures a bit of the Great Plains 

 of Colorado as ' near base level,' although 

 the contour lines indicate altitudes of over 

 4000 feet. (Monogr. XXII., U. S. Geol. 

 Survey, 1893, pi. viii.) Now it is true that 

 streams which have ceased the active deep- 

 ening of their vaUeys serve as local base- 

 levels for their ti-ibutaries — as Powell's ori- 

 ginal definition stated ; but it seems unad- 

 visable to speak of these streams as them- 

 selves having reached baselevel ; still less 

 is the country which slopes down to them 

 necessarily near ' baselevel.' If the term is 

 used in so general a sense as this, then an im- 

 portant feature in the development of rivei\s 

 will remain undistinguished bj' any special 

 name, and the attention of readers will not 

 be forcibly brought to it. It is well known 

 that when a river has cut down its valley 

 and reduced its velocity to such a value 

 that its capacity' to do work in transporting 

 waste is just equal to the work that it has 

 to do, any further change iu the profile of 

 the stream-channel can take place only as 

 fast as a change in the amount of land- 

 waste ofiered to the streams shall allow. 

 If the amount of waste slowly decreases, as 

 is commonly the case, the stream will slowly 

 assume a flatter and flatter slope (except so 

 far as the development of meanders may 

 lengthen its coui'se and thus retard the deep- 

 ening of its valley). If an increase in the 

 amount of waste takes place after equality 

 of capacity and task is reached, as some- 

 times happens, then the stream must ag- 

 grade its valley for a time. If the climate 

 of the region changes, a new slope may be 



