PLAINS OF ARID REGIONS 855 



formations whose deposition was contemporaneous with the ero- 

 sion of the peneplain, or in tlie form of fault-escarpments separat- 

 ing the uplifted from the non-uplifted areas. Moreover, it is ex- 

 tremely unlikely that the uplift of an extensive peneplain could 

 place it in so level a position that it should not suffer dissection 

 even by desert agencies ; hence a high-standing desert plain is best 

 accounted for by supposing that it has been leveled in the position 

 that it now occupies." (12: ^p8.) 



"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 transformed into a typical desert plain ; the danger of error 

 here is similar to that Ly which a peneplain, wave-swept and scoured 

 during submergence, might be mistaken for a normal plain of 

 marine abrasion." (I2:j9p.) 



"If an old rock-floored desert plain be gently warped or tilted, 

 marine submergence is not likely to follow immediately, but the 

 regvilar continuation of general degradation will be interrupted. 

 The 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 cer- 

 tainly 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 con- 

 tinuance 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 maiterials 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." {12:400-401.) 



Examples which serve to illustrate such deposits have been 

 described from South Africa (PassargQ) and West Australia, where 

 barren sandstones of continental orfgin surround the monadnocks 

 ("Inselberge"). Ancient examples seem to occur in the great 

 deposits of barren Uinta sandstones 12,000 to 14,000 feet thick in 

 some localities which lie at the base of the Palaeozoic series in the 



