EVALUATION OF STRATIGRAPIITC CRITERIA 4')T 



Modern examples outside of truly desert regions are found in the 

 southwestern part of France, in the vicinity of the coasts, on the shores 

 of Denmark and Prussia, and along certain stretches of the Atlantic 

 coast of the United States. These are sands which have been thrown up 

 by the waves or left by the retreat of the sea and show the widespread 

 character of wind action under climates far from arid. Ancient exam- 

 ples of wind-worn sands which have received recent study are the Saint 

 peter sandstone^"* and the Sylvania sandstone.^^ Of the origin of the 

 Saint Peter sandstone Berkey says : 



"The surface over which the S;unt Peter sniids were deposited was appar- 

 ently very uniform. If it had departed far from a low-lyin.2: phiin, we should 

 doubtless have many marks of it in erosion forms characteristic of such 

 elevation. On that plain, on its retreat, the sea spread great quantities of 

 sand and left the marginal supply (Basal sandstone margin) exiwsed to all 

 the transporting agencies. This the wind began to carry as dune sands along 

 the shore. Into these sands the rivers sank as they coursed toward the retresit- 

 iug sea, accomplishing little in erosion. At the maximum retreat of the sea, 

 it is the writer's belief that the Saint Peter sands presented the aspect of a 

 shifting-sand plain, perhaps akin to a desert in this one feature at least, 

 though not necessarily arid ; so the sands were washed out by the retreat of 

 the sea and thereby assorted, then worked many times over bj' the wind in the 

 absence of the sea, and thereby still more perfectly assorted, and finally in the 

 readvance of the sea much of it was again worked over a last time, thereby 

 reaching its present remarkable condition of purity. 



"That the Saint Peter sandstone was deposited in water and preserves chiefly 

 such structures as are connnon to (water laid) sediments is certain; that its 

 grains fall within the range of wind transportation and show characteristic 

 wind-worn surfaces is equally clear; that the formation relationships argue an 

 extensive retreat of the sea and an erosion interval is well supported — these 

 factors alone are sufficient to account for all the peculiarities and remarkable 

 characters of the Saint Peter, without any special agency." ^^ 



Concerning the Sylvania sandstone, Sherzer states that 



"This sand in its purity, degree of rounding, and assortment has attained a 

 degree of perfection that is being constantly approached, but never attained by 

 any known modern example. It out-Saharas the Sahara 1 This i)erfected 

 character of the Sylvania granules can be understood when the probable his- 

 tory is known, a lengthy and repeated buffeting with wind and wave, with no 

 opportunity for the accession of new mateiMal and with a mineral substance 

 inert to residual action." ^^ 



** C. P. Berkey : Paleogeograpliy of Saint Peter tirae. Bull. Geol. Soc. Aiueriea. vol. 

 17, 1900, pp. 229-250. 



35 W. H. Sherzer : Op. cit. 



" C. P. Berkey : Op. cit, pp. 246, 247. 



« W. H. Sherzer : Op. cit., p. 0.^1. 



