. Augustana Library publications. Scandinavians. l)l!IFTI.\(i ). 2:5 Table XIV. General Average of the Composition of Dune Sand (based on the averages for each locality where samples have been taken). Length or diameter in mm. Average. tures arrange tliemBelves in two series decrensing on cillicr side of the maximum. The coarse admixtures form a less rapidly decreasing- series than the fine, the former extend- ing over five grades in the general average and the latter over only three grades. The extension of either is di- minished by prolonged wind action, which results in more perfect el
. Augustana Library publications. Scandinavians. l)l!IFTI.\(i ). 2:5 Table XIV. General Average of the Composition of Dune Sand (based on the averages for each locality where samples have been taken). Length or diameter in mm. Average. tures arrange tliemBelves in two series decrensing on cillicr side of the maximum. The coarse admixtures form a less rapidly decreasing- series than the fine, the former extend- ing over five grades in the general average and the latter over only three grades. The extension of either is di- minished by prolonged wind action, which results in more perfect elimination of grains near either extreme. The occurrence of the maxi- mum at the same or nearly the same point in nearly all the dune sand taken at many different lo- calities, challenges our special notice. The size of a particle ca- pable of being transported by the current of a fluid varies as the sixth power of the velocity of the current. The diameter of the particles, therefore, varies as the square of the velocity. If the velocity is doubled, the diameter of particles transported may be increased four times. The range of velocities of dune-making winds, as usually measured, cer- tainly exceed a doubling of their speed, and it might be expected that the bulk of the sand, in some place at least, should consist of grains many times as large as in others. It may be that sometimes there is a scarcity of such sand for the wind to work on, but this will not alone account for the uniform composition of the dune sand. Wind velocities ai-e usuallv measured some 16â8 8-4 4â2 2-1 1- T2"' 1 _ or 1 _ â 1. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Augustana College and Theological Seminary (Rock Island, Ill. ); Augustana College (Rock Island, Ill. ). Library. Rock Island, Ill. : Augustana College and Th
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