THE GEOGRAPHICAL CYCLE IN AN ARID CLIMATE 399 



Whether an appropriate deposit of wind-borne waste is to be found 

 on neighboring regions is not yet made clear. 



It should not, however, be overlooked that there is some danger of 

 misreading the history of a depressed desert plain which has been 

 by a moderate amount of normal weathering and erosion transformed 

 into a normal peneplain; and of an uplifted peneplain which has 

 been by a moderate amount of arid weathering and erosion trans- 

 formed into a typical desert plain; the danger of error here is similar 

 to that by which a peneplain, wave-swept and scoured during sub- 

 mergence, might be mistaken for a normal plain of marine abrasion. 

 The consequences of error in these cases of actual plains are, how- 

 ever, not so serious as in those which may arise in connection with 

 dissected plains; for this class of forms is of common occurrence, 

 and mistakes in explaining their origin as uplifted peneplains or as 

 changed-climate desert plains might therefore be of frequent and 

 widespread occurrence. It is therefore desirable to search out 

 those features by which normal peneplains, uplifted and dissected, 

 may be distinguished from desert plains, dissected after a change 

 to humid climate. 



If a normal peneplain be uplifted, its already adjusted streams 

 will carry their adjustments still farther in the new cycle. The high 

 degree of adjustment of streams to structures in the Pennsylvania 

 Appalachians and in the mediaeval coastal plain of central England 

 therefore suggests that the former surface of truncation, beneath 

 which the present lower lands have been etched out, was a normal 

 peneplain, uplifted. If a normal peneplain be tilted, its depressed 

 part will soon be submerged and covered with marine deposits; and 

 this part may, by later uplift, be associated with the elevated and 

 dissected part. The marine deposits of our Atlantic and Gulf 

 coastal plain, certain basal strata of continental origin excepted, 

 seem to lie upon a depressed part of the Appalachian peneplain, 

 and thus confirm the evidence of normal baseleveling derived from 

 the adjusted drainage of the uplifted and dissected part of the same 

 peneplain; the basal strata just mentioned contain fossil land plants 

 of normal climate and confirm the conclusion. The now dissected 

 uplands of Brittany and of the Ardennes are adjoined or overlapped 

 by marine deposits which give strong suggestion of normal pene- 



