THE GEOGRAPHICAL CYCLE IN AN ARID CLIMATE 401 



patches and veneers of waste will be washed from the higher to the 

 lower parts of the warped surface; the higher parts, having an 

 increased slope, might be somewhat dissected, and would certainly 

 be exposed to more active degradation than before, until they were 

 worn down to a nearly level plain again. The lower parts would 

 receive the waste from the higher parts, and the continuance of this 

 process of concentration would in time cause the accumulation of 

 extensive and heavy deposits in the lower areas. Such deposits 

 will be, as a rule, barren of fossils; the composition, texture, and 

 arrangement of their materials will indicate the arid conditions 

 under which they have been weathered, transported, and laid down; 

 their structures will seldom exhibit the regularity of marine strata, 

 and they may reach the extreme irregularity of sand-dune deposits. 

 If warping continues, the desert deposits may gain great thickness; 

 their original floor may be depressed below sea-level, while their 

 surface is still hundreds or thousands of feet above sea-level. 



Passarge gives a number of instances which he groups under the 

 Banda type (b, p. 200) that seem to illustrate this phase of the arid 

 cycle, although he ascribes the barren sandstones of this type to a 

 weakening in the activity of the winds, rather than to a tilting of the 

 region. Here the upper parts of monadnocks — Inselberge — rise 

 above a broad deposit of barren continental sandstones; the inter- 

 mont plains, being buried, are matters of interference. Examples of 

 this type are mentioned in West Australia as well as in Africa. 



If a change from an arid toward a moister climate causes a drainage 

 discharge to the sea, a dissection of the plain will ensue. The valleys 

 thus eroded cannot expectably exhibit any great degree of adjustment 

 to the structures, because the stream courses will result from the 

 irregular patching together of the pre-existing irregularly disintegrated 

 drainage. This peculiar characteristic, taken together with the 

 absence of neighboring uplifted marine deposits, will probably suffice 

 in most cases to distinguish desert plains, dissected by a change to a 

 moister climate, from peneplains dissected in consequence of upilft; 

 but there still might be confusion with peneplains dissected by super- 

 posed streams. 



Passarge gives two types of desert plains with a modified climate. 

 The first or Kordofan type (b, p. 200) is marked by a slight increase 



