EVALUATION OF STRATJORAPTlir' CRITERIA 4o() 



rivers and playa lakes could lay down. The writer has argued else- 

 where that red as a color of consolidated formations may arise by dehy- 

 dration of the iron during the diagenesis as well as during the deposition 

 of the sediment and is liable to be produced in rocks as the result of any 

 climate which permits occasional aeration of the alluvial soil.^** Fur- 

 thermore, the study of modern examples readily shows that fine-grained 

 sandy alluvium may be modified by wind within the same broad climatic 

 limits and does not necessarily imply desert climates. This is owing to the 

 fact that a desert condition may be related to a barren sandy soil as well 

 as to an excess of evaporation over precipitation. A sandy alluvium which 

 permits the rain to run through it and which is too coarse to permit 

 capillary retention of water may give rise to a local desert even with a 

 high rainfall, and it is clearly erroneous to describe such conditions as im- 

 plying a desert climate. For examj^le, under the semi-arid climate of 

 western Kansas and Nebraska the fine sands laid down by the Tertiary 

 rivers are broadly reworked at present by wind and the surface of the land 

 is ridged with dunes, yet the land supports great herds of cattle and was 

 but recently the home of myriads of buffalo. In central Kansas sand is 

 swept by wind from the bed of the Arkansas over the plains to the east 

 to such an extent that the region is used as an illustration of dune topog- 

 raphy by Chamberlin and Salisbury in their Geology.^® This is in a 

 region in which the mean annual rainfall is between 20 and 30 inches 

 per year, with a maximum in early summer, but dry late summer. Still 

 more significant are the sandy barrens of such regions as northern Prus- 

 sia and Long Island and other areas of sand which were laid down as 

 fluviatile outwash deposits from the Pleistocene glaciers.**' The rainfall 

 and temperature of these regions is such that if the loose sand can be 

 protected from wind and sun action until a vegetable cover is established 

 it will become reclaimed. Under the conditions of river building, con- 

 nected with wandering channels and a continual supply of sand derived 

 from them, the reclamation would apparently be more difficult. In 

 earlier geologic ages the vegetation was presumably less specialized for 

 such conditions and less efl^ective in preventing wind action. Although 

 its presence in moving and rounding the sand shows local desert condi- 

 tions, it does not necessarily imply that such existed outside of the region 

 of the deposit nor that there was a deficiency of rainfall. 



Eolian action in arenaceous river deposits is thus seen to be peculiarly 



="* Relations between cHmate and terrestrial deposits. Journal of Geology, vol. xvi, 

 1908. pp. 28.^)-20:i. 



3-' Vol. i. 1004, pi. II. fig. 2, p. :}1. 



^ For an illustration from Connecticut see nowninn. Forest Physiography, 1911, p, 

 GGl. John Wiley & Sons. 



