^OLIAN TYPES 



643 



minerals beginning tlieir processes of decay. If iron is present in these 

 minerals or is secondarily introduced in any way^ the quartz granules 

 will become coated with yellow, brown, or red oxide. AYhat is apparently 

 such a sand has been described by Phillips under the title, "The red 

 sands of the Arabian Desert.''^* The surface features of this desert 

 appear to be in a state of repose, as evidenced by the sprinkling of vege- 

 tation, by objects left on the surface remaining uncovered for 3'ears and 

 the fact that the same landmarks can be constantly used in crossing. The 

 quartz grains are well rounded and coated with a deposit of ferric oxide, 

 giving the sand a light red color, described as almost crimson when wet 

 with dew in the early morning. The English Bunter sandstones, of 

 Triassic age, have been assigned an seolian origin by Phillips and are 

 plainly of the residuo-geolian subtype, judging from the following de- 

 scription : 



"Reddish-brown friable beds, possessing but little cohesion, and of which the 

 constituent grains are all so completely rounded, that the disintegrated sand 

 flows between the fingers as readily as shot. . . . These grains, of which 

 the majority are quartz, are so rounded as to represent miniature pebbles, 

 while a few, consisting of partially decomposed felspar, are often corroded into 

 deep cavities on one or more of their sides. "^^ This is one of the so-called 

 "millet-seed" types of sandstone. 



As the result of stream or wave action on an geolian deposit, ancient or 

 modern, the aqueo-?eolian subtype of sand would be formed. If kept 

 free from admixture with other aqueous material, which would not ordi- 

 narily be the case, it is not apparent that any special change would occur 

 in the character of the granules. If found in the water itself, the more 

 perfected character of the granules would suggest an geolian origin, while 

 if already deposited the nature of the stratification, the character of the 

 cement, or the presence of water fossils would point toward its aqueous 

 relationship. This is illustrated very satisfactorily by portions of the 

 Sylvania formation, to be presently described. 



Oeganic Sa;n-d Type 



Unless it is remembered by the reader that the classification here 

 adopted is based on the agency or agencies concerned in sand production, 

 and not on its composition, the term organic will prove misleading.^^ 



3* Quarterly Journal of the Geological Society of London, vol. 38, 1882, p. 110. 



35 Phillips : On the constitution and history of grits and sandstones. Quarterly 

 .Tournal of the Geological Society of London, vol. xxxvii, 1881, pp. 12-13. 



36 It may he noted, however, that sand of organic composition. If found to exist, 

 would also he Included under this same heading. It is conceivable that granules of 

 suitable texture might he locally segregated consisting of coal, asphaltum, fossil spores, 

 amber, evaporated petroleum, etc. 



