AQUEOUS TYPES 635 



left in the river sands taken from points nearest the sea was 18 per cent, 

 while the neighboring sea sands were found to contain bnt 10 per cent 

 (page 149). The common minerals, softer than the feldspars, would be 

 disposed of still more promptly, and there results a gradual concentra- 

 tion of the quartz granules because of its hardness, specific gravity, lack 

 of cleavage, insolubility, and ability to resist decomposition. AYork of a 

 similar nature has been done also by Walther in the way of showing that 

 the softer and more decomposable minerals are slowly eliminated in the 

 course of a stream leading to a concentration of quartz. In proportion 

 to the amount of water action to which they have been subjected these 

 quartz grains become smoothed, present rounded edges and corners, and 

 assume subangular outlines. By subjecting angular fragments derived 

 from crushed granite to an experiment in which the distance traveled 

 could be approximately determined, Daubree found that in a distance of 

 about 151/2 miles these fragments were indistinguishable from common 

 river sand. The investigations of this able experimenter showed further 

 that granules .1 millimeter in diameter will float in feebly agitated w^ater, 

 from which he concluded that grains of this size and less could not be 

 mechanically rounded by water action.^" When such are found in aqueous 

 deposits the inference is that they are of other origin. 



An interesting pure gray sand, which seems to have been due to very 

 long continued water action, is found on the Gulf of Mexico coast, Es- 

 cambia County, Florida. There is scarcely a fragment left of any min- 

 eral other than quartz showing practically perfect concentration, while 

 the granules evince long continued wear, but are still subangular in gen- 

 eral outline rather than subspherical or ellipsoidal (see figure 4, plate 

 44) . This sand is briefly described under the head of "Gray Sand^^ in the 

 Second Annual Eeport of the Florida Geological Survey, 1909, page 152. 

 A mechanical analysis of this sand by the IT. S. Bureau of Agriculture 

 shows that practically all material below .1 millimeter has been removed 

 (presumably by assorting action), and that the granules range from .1 

 millimeter to 1 millimeter in diameter, averaging from .25 to .50 milli- 

 meter.^^ It would be of interest to know the distance that this material 

 has been transported and the original source of it, but so far this is un- 

 known. Under date of May 14, 1910, State Geologist E. H. Sellards 

 writes that he regards the mantle of sand over the interior of the state of 

 Florida as residual and resulting from the decay of originally existent 

 sand-bearing formations. As to that of the highlands of Escambia 



1^ Geologic Bxpgrimentale, p. 256. 



1* Reported in correspondence by E. E. Free, physicist of the department. 



