CHAPTER V. 
THE SANDS. 
Origin of Sand—Sand now Carried to the Sea—Beach Sands of Northern 
Africa—Sands of Egypt—Sand Dunes and Sand Plains—Coast Dunes— 
Sand Banks—Character of Dune Sand—Interior Structure of Dunes— 
Geological Importance of Dunes—Dunes on American Coasts—Dunes 
of Western Europe—Age, Character, and Permanence of Dunes—Dunes 
as a Barrier against the Sea—Encroachments of the Sea—Liimfjord— 
Coasts of Schleswig-Holstein, Netherlands, and France—Movement of 
Dunes—Control of Dunes by Man—Inland Dunes—Inland Sand Plains. 
Origin of Sand. 
Sanp, which is found in beds or strata at the bottom of the 
sea or in the channels of rivers, as well as in extensive de- 
posits upon or beneath the surface of the dry land, appears to 
consist essentially of the detritus of rocks. It is not always by 
any means clear through what agency the solid rock has been 
reduced to a granular condition; for there are beds of quart- 
zose sand, where the sharp, angular shape of the particles ren- 
ders it highly improbable that they have heen formed by 
gradual abrasion and attrition, and where the supposition of a 
crushing mechanical force seems equally inadmissible. In 
common sand, the quartz grains are the most numerous; but 
this is not a proof that the rocks from which these particles 
were derived were wholly, or even chiefly, quartzose in charac- 
ter; for, in many composite rocks, as, for example, in the gran- 
itic group, the mica, felspar, and hornblende are more easily 
decomposed by chemical action, or disintegrated, comminuted, 
and reduced to an impalpable state by mechanical force, than 
the quartz. In the destruction of such rocks, therefore, the 
quartz would survive the other ingredients, and remain un- 
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