. Nature . mound (Fig. i)—in some caseswith serious consequences. Dr. Vaughan Cornish, whohas made a special study of this subject, has clearly proved, 1 Pi-cours- deliveiel at he Institution on Friday, February 11,bv Mr. tharlts E. S. PhHip-;. 256 NATURE [August 25, 1910 however, that the formation of a sand dune is very fre-quently due to wind eddies. The second photograph was,in fact, talcen by him in Egypt, and depicts the steady,irresistible march of millions of tons of sand, encroachingupon and slowly burying casuarina trees (Fig. 2). To come nearer home, the seriousness of probl
. Nature . mound (Fig. i)—in some caseswith serious consequences. Dr. Vaughan Cornish, whohas made a special study of this subject, has clearly proved, 1 Pi-cours- deliveiel at he Institution on Friday, February 11,bv Mr. tharlts E. S. PhHip-;. 256 NATURE [August 25, 1910 however, that the formation of a sand dune is very fre-quently due to wind eddies. The second photograph was,in fact, talcen by him in Egypt, and depicts the steady,irresistible march of millions of tons of sand, encroachingupon and slowly burying casuarina trees (Fig. 2). To come nearer home, the seriousness of problems arisingout of this state of things may be illustrated by two photo-graphs obtained recently at Southport, in Lancashire. Inthe first one (Fig. 3), the bacli garden of a newly builthouse is nearly buried beneath the enormous hill, whichwill probably soon cover the whole property. The second(Fig. 4) shows that the familiar appearance of a sandybeach at low vifater, with regular lines of ripples, may be. produced by the direct action of the wind, and, incidentally,the utter futility of constructing an esplanade in such aneighbourhood. All these phenomena depend, in somemeasure, upon the size, weight, and shape of the sandgrains themselves. Silica, a substance which occurs in numerous impureforms, and constitutes a large portion of the rock massesknown to geologists, is also to be found in a pure stateas crystalline quartz. Here is an actual specimen about18 inches long, which, together with the beautiful groupof quartz crystals by its side, known as amethysts (andtinted, probably, by a trace of organic matter), are theproperty of this institution. Sand, therefore, being theresult of rock disintegration, assisted by the grinding actionNO. 2130, VOL. 84] due to the motion of wind or water, varies in composition in different localities. The next slides are photomicrographs taken with a low-power objective. They represent some grains of sandfound at Charlton and the Isle of Eigg
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Keywords: ., bookcentury1800, booksubjectnaturalhistory, booksubjectscience
