OLDER EOLIAN DEPOSITS 565 



same thing is true of coatings of vegetation which are buried by the 

 readvancing sands. In the sand dunes of Cape Cod many such ex- 

 amples are found, and the same is true for the sand hills of Ne- 

 braska. Indeed, this may be seen in almost all coastal dunes where 

 vegetation has gained a temporary foothold. Such sands would 

 thus become lignitic, and the fragments of lignitized and broken 

 wood may be scattered and incorporated in the sands over a wide 

 area. The lignitic sands of the Raritan formation of New Jersey 

 apparently had such a history. 



Transgrcssivc Relation of Dune Sands to Subjacent Formations. 



The southward transgressing dunes of the Kara Kum or Trans- 

 caspian desert spread layers of sand over the older fluvial or marine 

 deposits. The pure quartz sands of the Libyan desert, derived from 

 the disintegration of the Nubian sandstone a hundred miles away, 

 transgress across the floor of Cretacic and Tertiary limestones, and 

 the wenthered-out fossils of these formations are enclosed in the 

 basal part of the sands. 



In the profile of the earth's crust many cases of such trans- 

 gressive relation of unfossiliferous sandstones upon fossiliferous 

 marine deposits are found. Examples are the St. Peter on the 

 Beekmantown limestone, the Sylvania on the Monroe dolomites, 

 the Bunter Sandstein u])on the marine Zechstein, the Keuper upon 

 the Muschelkalk and many others. Such deposits point strongly to 

 an origin comparable to that of modern desert sands which overlie 

 marine sediments of an earlier agre. 



Examples of Older Eolian Deposits. 



The Loess as an Example of a Dust Deposit. The loess is a 

 continental deposit of loosely arranged, angular grains of calcare- 

 ous silt loam, typically intermediate in fineness between sand and 

 clay and of remarkably uniform mechanical composition. Normally 

 it is without stratification, and breaks off in vertical slabs, with the 

 result that perpendicular cliff's arc formed. Loess was first dc- 

 scri1)ed from the valley of the Rhine, but is also known from south- 

 eastern Europe, from North America, and especially from China, 

 where it was fully described by von Richthofen (42). Here the 

 loess sometimes has a thickness of a thousand feet or over, and is 

 believed to be primarily the disintegrated rock material brought by 



