222 M. R. CAMPBELL EROSION AT BASELEYEL. 



The object of this paper is to present some facts which appear to have 

 a bearing on this important question, and to suggest a theory regarding 

 the processes of erosion at or near baselevel. 



Local Baselevels in the Appalachians. 



general characteristics in the areas observed. 



During the progress of regular work in the Appalachian coal-field the 

 writer has had the pleasure of observing several well marked baselevels 

 which are doubtless of recent formation and which present some pecu- 

 liar features that seem worthy of careful consideration. The most strik- 

 ing feature, and one which seemed to be generally characteristic, is the 

 sharp line of demarkation between the level floor of the basin and the 

 gentle slopes usually surrounding it. 



Figure i. — Ideal Cross-section of a local Basin in West Virginia. 



Figure 1 is a diagrammatic cross-section of one of these basins, in which 

 the slopes A B and CD are seen to join abruptly the level floor B C. In 

 some cases the abrupt termination of the erosion slope can be accounted 

 for by the presence of a stream near that side of the basin, but in many 

 cases there seems to be no relation whatever between the location of the 

 stream and the sharp cutting at the foot of the slope, for the line of sepa- 

 ration can be traced continuously around all of the sinuosities of the 

 corrugated erosion slope. 



Figure 2 is an ideal sketch of the conditions observed in a number of 

 instances. 



In many cases the disposition of the hard and soft beds is such that 

 the sharp line of demarkation appears, at first sight, to be due to this 

 condition rather than to the general process of erosion ; but more ex- 

 tended observations suggest that it is a general condition and not de- 

 pendent upon the local character or attitude of the strata. The rocks 

 are generally horizontal in this region or with scarcely appreciable dips; 

 consequently if a hard bed of sandstone interrupt the development of 

 any of the drainage lines, the basin which forms above the barrier will 

 necessarily be floored by the same bed, and there will be a decided differ- 

 ence in the rate with which erosion operates on the floor and on the sides 

 of the basin. In several instances, however, the bed forming the barrier 

 is slightly folded in such a manner that it does not appear above the 



