22 GENESIS AND DEVELOPMENT 



of water, while as soon as the foot is lifted the original dull color is 

 quickly resumed. 



Very fine sand is angular, and the rounding by water is produced 

 only when the strength of the current is not sufficient to keep the grains 

 suspended, but yet capable of moving them. The specific gravity of the 

 volume of sand is always smaller than that of the solitary grains. The 

 latter leave between each other spaces which are filled with air and 

 water; if all the grains were of the same size and exactly spherical, 

 the specific gravity of the volume of sand would be independent of the 

 absolute size of the grains, but as soon as grains of different sizes are 

 mixed, the small grains fill the spaces between the larger and hence 

 increase the specific gravity. This latter is also, the mineral character 

 of the grains being equal, higher the more dissimilar the grains are. 



The texture of the sand in each locality depends entirely upon the 

 nature of the rocks from which it was originally derived. Through 

 having a comparatively large mixture of different sizes, and consisting 

 of the most different minerals of different specific gravity, beach sands 

 exhibit considerable differences in texture. On almost every non-rocky 

 coast, however, some kind of accumulation of fine grained quartz sand 

 can be noticed. 



By quartz sand we understand a soil consisting mainly of white or 

 yellowish quartz grains, among which only very seldom any organic mat- 

 ter is distributed. Being conspicuously free from foreign constituents, 

 quartz sand is very uniform. It is generally believed that the pure 

 quartz sand on marine shore is a special result of the action of the sea. 

 This is, however, not the case. I have examined many samples of the 

 littoral sediments on different coasts, but never found the clean white 

 quartz sand of the beach occuring on the bottom of the sea. On the 

 contrary, the sandy sediment under water is impure, mixed with organic 

 matter, and highly colored. As soon as the sand is thrown ashore by 

 the wave and current action, and left at the water level, it is picked 

 up by the wind and carried inland. And if we observe the sand of the 

 beach from the edge of the water landward, we will find that it becomes 

 cleaner the further it is from the sea. This fact is mentioned by several 

 authors; for instance, Serres,^ who speaks of it in discussing the 

 French Mediterranean coast. Beach formations are very irregular in 

 stratification in their upper portions, where they are made by the toss 



1) Marcel de Serres: Der Treib- und Flugsand des MittellSndischen Meeres. 

 Peterm. Mitth. V : 197198. 1859. 



