ABSTRACTS 323 



slopes is removed by solution and does not accumulate on the surface 

 of the plain. 



This conclusion is still further substantiated by the fact that in the 

 local basins observed in the coal field, the surrounding slopes are 

 sharply separated from the bottoms of the basins, showing that even in 

 these small examples there is some action going on by which the waste 

 is carried off in solution leaving the floor of the basin unobstructed 

 and a nearly perfect plain. 



If these conclusions are correct, the baseleveling epochs of the past 

 njay have been marked by very completely formed plains, and the 

 slopes of the unreduced areas may have been sharply separated from, 

 instead of blending with, the surface of the plain. 



Origin of Certain Topographic Forms. By M. R. Campbell. 



The recognition of apparently abnormal physiographic forms in 

 limited areas has induced the writer to undertake an investigation of 

 their probable cause. Since the abnormal types are limited in their 

 geographical distribution, they are doubtless caused by local variations 

 in some of the conditions governing erosion. Climate and rock char- 

 acter are variable, but changes in them could not produce tne forms in 

 question. Declivity must be accountable. Declivity may be changed 

 by crustal movements, but those which operate over a broad area 

 change the declivity as a whole, and hence cannot produce local varia- 

 tion. Movements which are limited in their extent are the ones which 

 must be looked to for local variation and the production of abnormal 

 forms. Local uplifts may result in the production of normal faults, 

 monoclinal folds, symmetrical folds, and dome-shaped uplifts ; each of 

 these structural forms, when produced during the final stage of an 

 erosion cycle, — for at that time alone will they introduce new erosion 

 conditions, — will be marked by physiographic features peculiar to 

 itself. 



The production of a scarp from a monoclinal fold is perhaps the 

 most ren:arkable form, and it is due to a peculiar combination of slow, 

 regular uplift, homogeneous rocks, and baseleveling conditions outside 

 of the area affected bv the uplift. 



This principle is applied to the solution of the Blue Ridge scarp in 

 North Carolina, and it is shown that the physical features of that 

 region could have been produced by a monoclinal uplift in a broad 



