OF SAND FOBMATIONS ON MARINE COASTS. 29 



If we consider the general appearance and composition of the drift 

 sands we find that they consist in a preponderating degree of somewhat 

 rounded grains of quartz sand with only a very small percentage of 

 other materials. The admixture consists primarily of felspar, of mica, 

 and of various other minerals, such as hornblende, augite and granite, 

 and to some extent of lime, mostly in form of fragments of shells. 



In a crystallinic rock, such as granite, we find that the different con- 

 stituents, felspar, quartz and mica, are present in isolated crystals. 

 As soon as these elements are separated from each other, they acquire 

 a granulated form and constitute what we call quartz sand. The grains 

 of felspar and mica act, however, in a different way than those of quartz, 

 the latter representing crystallographically only one or a few individuals, 

 while felspar and mica consist of many thin lamellae. Hence, when 

 exposed to the decomposing agencies, disintegration of felspar and mica 

 is much more intensive than that of quartz. The different particles of 

 sand are moved more rapidly by the wind the lesser their gravity in 

 proportion to their surface. Mica is so light that the least gust of 

 wind carries its thin lamellae, away, and it is further so brittle that 

 it is easily broken into small fragments against other sand particles. 

 The same can be said of felspar, although, perhaps, in a less degree. 

 Here we also have to consider the chemical facility for decomposition. 

 During the night and in the dewj^ mornings, the felspar which has been 

 opened through the many capillary spaces is chemically decomposed by 

 the moisture, while the quartz has a greater resistance against this 

 agency. Consequently the older the dune sand is and the longer time 

 and water have exerted their influence, the less felspar will be found 

 in it and the more dominant is the quartz over the other minerals. 

 As a rule, all the sand grains, however, exhiljit more or less the rounded 

 appearance due to attrition and weathering. 



Besides the sand, the wind carries all kinds of light plant remains, 

 thin shells, dry crabs, dead and living insects, and similar particles. 

 All these temporary constituents of the dune are, however, insignificant 

 in comparison with the sand, and are usually so rapidly decayed that 

 they are seldom found in the deeper parts of the dune. The separate 

 gi'ains are mostly covered with a fine mold, in part due to the decomposi- 

 tion of the above organic remains, on which depends the fertility of 

 the sand. The drift sand, though varied with a sprinkling of somewhat 

 rare grains of darker colored substances, is generally a mass of a light 

 color. 



The stratification of dunes is usually very mixed, and in the same 



