OLDER DUNE-LIKE DEPOSITS 



571 



dunes. This is the White Cliff sandstone of southern Utah, the 

 origin of which as a subaerial dune sand deposit can hardly be 

 questioned. 



The Triassic shows many examples of dune sands, commonly 

 much iron-stained, though these are generally associated with fluvia- 

 tile and sometimes lacustrine deposits. They have been recognized 

 in both America and Europe. In the Triassic strata of England 

 and the Elgin sandstone of Scotland this eolian origin seems to be 

 well indicated. 



In the Palaeozoic occur many deposits which bear the earmarks 

 of an eolian or dune origin. Among those that may be cited in this 

 connection are the white dune sands beneath the Magnesian lime- 

 stone of England and tlie similar beds of "Weissliegende" in Ger- 

 many; the Kanab and Colob formations (probably Permic) of 

 southwestern Utah and northwestern Arizona ; parts of the Old Red 

 sandstone of Britain ; and the Sylvania and St. Peter sandstones of 

 Siluric and Ordovicic age, respectively, in the L^nited States. The 

 Sylvania sandstone may be taken as a typical example of this kind 



Fig. 120. Cross-bedding in Sylvania Sandstone (Siluric). (After Sherzer 

 and Grabau.) Scale i :8o. 



of deposit (Sherzer and Grabau-45 : 72). This rock consists of 

 well-rounded grains of quartz, of nearly uniform size, and seldom 

 carrying over 3 per cent, impurities, these being mainly calcium and 

 magnesium carbonates. In fineness, uniformity of size, roundness 

 of grain and purity of composition it outrivals the most typical 

 modern desert sands, such as are found in various parts of the 

 Libyan and Sahara deserts. Cross-bedding of the eolian type is 

 well developed, as shown by some of the accompanying sketches 

 (Figs. 119, 120). Altogether this deposit ranges in thickness up 

 to 300 feet, and is distributed over an area of more than six degrees 

 east and west longitude and four degrees north and south latitude. 

 It may be regarded as one of the best examples of a Palaeozoic 

 dune sand deposit known to us. 



