. Elements of geology, or, The ancient changes of the earth and its inhabitants as illustrated by geological monuments. Geology. 20 EIPPLE MAEK. [Ch. IL at low tide, seems to originate in the drifting of materials along the bottom of the water, in a manner very similar to that which may explain the inclined layers above described. This ripple is not entirely confined to the beach between high and low water mark, but is also produced on sands which are constantly covered by ; Similar undulating ridges and furrows may also be sometimes seen on the surface of drift snow and blown sand.
. Elements of geology, or, The ancient changes of the earth and its inhabitants as illustrated by geological monuments. Geology. 20 EIPPLE MAEK. [Ch. IL at low tide, seems to originate in the drifting of materials along the bottom of the water, in a manner very similar to that which may explain the inclined layers above described. This ripple is not entirely confined to the beach between high and low water mark, but is also produced on sands which are constantly covered by ; Similar undulating ridges and furrows may also be sometimes seen on the surface of drift snow and blown sand. The following is the manner in which I once observed the motion of the air to produce this effect on a large extent of level beach, exposed at low tide near Calais. Clouds of fine white sand were blown from the neighboring dunes, so as to cover the shore, and whiten a dark level surface of sandy mud, and this fresh covering of sand was beauti- fully rippled. On levelling all the small ridges and furrows of this ripple over an area of several yards square, I saw them perfectly restored in about ten minutes, the general direction of the ridges being always at right angles to that of the wind. The restoration began by the appear- ance here and there of small detached heaps of sand, which soon lengthened and joined together, so as to form long sinuous ridges with intervening furrows. Each ridge had one side slightly inclined, and the other steep ; the lee-side being always steep, as b, c,—d, e ; the windward- side a gentle slope, as a, b,—c, d, fig. 9. When a gust of wind blew. with sufficient force to drive along a cloud of sand, all the ridges were seen to be in motion at once, each encroaching on the furrow before it, and, in the course of a few minutes, filling the place which the furrows had occupied. The mode of advance was by the continual drifting of grains of ^and up the slopes a b and c d, many of which grains, when they arrived at b and d, fell over the scarps b c a
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Keywords: ., bookcentury1800, bookdecade1860, booksubjectgeology, bookyear1868
