CONCEXTRATION SAND TYPE 647 



linie-secreting plants. Portions are so firml}^ cemented into a coqnina- 

 ceous sandrock as to be ntilizable for building purposes. The Bahamas 

 furnish similar deposits; also the shores of the Eed and Arabian seas. 

 The southwestern coast of Gahva}^^ Ireland, contains low dunes made up 

 largely of foraminiferal material^ with other calcareous fragments, de- 

 scribed by Evans, along with other similar deposits. ^^ The author con- 

 sidered that the Great Oolite formation (Jurassic) of England had re- 

 sulted from the accumulation of wind-blown oolitic granules, interbedded 

 with littoral deposits (page 580). 



CONCENTRATIOX SaND TyPE 



This term, perhaps not the happiest that can be found, is used to 

 designate a type of sand resulting from the concentration of solutions 

 l)y evaporation, or by chemical action whereby the same result is achieved. 

 From this method of formation the material will be generally crystalline 

 in structure, the growth taking place from within, outward about a cen- 

 ter, so that the connotation of the term selected for the type is not in- 

 appropriate. In this manner of formation the concentration granules 

 are distinguished from all other types, except certain ones l^elonging to 

 the organically formed division. When these minerals are deposited in 

 granular condition, or reduced to such, they may be collected by wind 

 action and form extensive deposits in arid regions, ^ear Alamogordo, 

 ^ew Mexico, there occurs an immense deposit of gypsum sand reported 

 to be some 300 square miles in area. A sample shows it to be practically 

 pure gypsum, of creamy white color, the granules being very generally 

 rounded, but where broken along the cleavage planes showing fresh edges 

 (see figure 5, plate 46). Crushed between the fingers it is reduced to 

 fine, angular fragments. These deposits have been recently figured and 

 described b}' MacDougal in publication Xo. 99 of the Carnegie Institu- 

 tion, 1908, page 11, and a chemical anatysis given. In the paper just 

 referred to by Eussell smaller but similar gypsum dunes are mentioned 

 as located near Fillmore, Utah. Deposits of salt in granular condi- 

 tion may form in arid regions around the margins of salt lakes, such as 



^1 Evans : Mechanically formed limestones from Junagarh and other localities. Quar- 

 terly Journal of the Geological Society of London, vol. Ivi, 1900, p. 559. This paper 

 contains a full list of references treating of seolian action on calcareous fragmental 

 deposits. See also, in same volume, Chapman's paper, "Notes on the consolidated 

 seolian sands of Kathiawar," p. 584. In a paper entitled Subaerial deposits of the arid 

 region of North America, Russell mentions low dunes in the Carson Desert of Nevada 

 made up entirely of casts of a small crustacean — Cypris. Geological Magazine, new 

 series, vol. vi, 1889, p. 289. 



