Abstract

Important literature relating to the rounding of sand grains is reviewed with comments. Methods of transportation of sands in suspension and traction are examined and it is stated that suspension transportation in either water or wind is not effective in producing rounding of transported particles. Aqueous transportation by traction is considered for streams and on beaches and eolian transportation in any environment. It is concluded that stream traction transportation does not favor rounding of sand grains, that wave traction transportation is not very if at all effective in producing rounding on sands of the specific gravity, solubility, and hardness of quartz on grains less than 1/4 mm. in diameter and is not very effective on grains in the 1/4 to 1/2 mm. grade, is considerably effective on grains in the 1/2 to 1 mm. grade, and increasingly effective with increase in dimension. Rounding by wave traction transportation is readily produced on minerals of high specific gravity as magnetite and zircon to dimensions as small as [1]/[16] mm. in diameter, and that any rounding of sand grains by aqueous traction transportation requires travel of many thousands of miles. It is concluded that eolian traction transportation is more effective in producing rounding than aqueous traction transportation for the same distance traveled, and that grains less than 1/4 mm. in diameter of the hardness and specific gravity of quartz may be rounded in such transportation. Eolian traction transportation can produce frosted surfaces on grains less than 1 mm. in diameter. Aqueous traction transportation can not produce frosted surfaces on grains less than 1 mm. in diameter, rarely produces such surfaces on grains in the 1 to 2 mm. grade, and readily does so on grains larger than 2 mm. and to higher degrees with increase in dimension. It is insisted that most sand assemblages are composed of grains with extremely varied and often complex histories, and that these histories must be considered in any examination of sands for discovery of facts of sedimentational significance.

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