consequently will heap the beach down wind against the groin. When the wave falls parallel to the shore it forms the lower shore in ridge and furrow running straight across the shore to the sea. But as the wind blows the wave flows and as the wave flows the beach goes, and in general the wave breaks on the shore obliquely. But it always recedes from the shore straight, consequently every pebble that is moved travels along the shore with the wind or at least with the wave. On all large beaches of shingle two or three terraces may in general be seen, owing to the movement of beach at the different high water marks at spring and neap tides, and also to the accidental differing height and power of the waves at high water, and on the same groin these terraces may often be seen to have been heaped while travelling in opposite directions, according as opposite winds have prevailed. It requires an oblique gale of wind at high water at the highest spring tide to smooth the entire beach. Groins are generally tied by cross beams from the side of the greatest exposure to wind. These beams become permanently imbedded and hold the groins by tension. So that the greater the weight on the groin the greater the power which holds its ties, and the weight against the groin is thus most ingeniously made to hold itself up. When the pebbles have risen as high as the groins they flow over the groins. But they never heap on the leeward side. On the contrary, the sea always digs deepest on the leeward side of the groins. For the oblique wave flows freely up the heaped windward side and over the groin and falls with impact on the unheaped leeward side and would undermine props of the groin. Thus the beach on the leeward side of a groin recedes from the sea by denudation, and the beach on the windward side of a groin advances into the sea by heaping, and the oblique wave is constantly at work to bring the line of beach parallel to itself. sizing of sea Shake the sugar-basin. The large lumps come Sorting and to the top; the fine sugar goes to the bottom: beach. because the small grains have a greater facility in passing downward between the large lumps than the large lumps have. From the sugar-basin reason, when the field has been well worked and harrowed, all the surface flints are above the surface. Abstract the motion and they have a tendency to sink, I think as low as the bottom of the soil. From this sugar-basin reason, as the largest pebbles are always on the surface of the beach, they are the first to be struck by the wave, and they are rolled to the top of the beach, and this sugar-basin reason sifts, sorts, and sizes the beach on every seashore of the wide, wide world. In Blown sand. screening sand or gravel the largest grains or pebbles run down to the lower part of the surface. On the shore it is the upward stroke of the wave which places the largest pebbles on the upper part of the surface, and as extremes meet, the lightest floatage and the heaviest drift travel together up the shore in each flood tide, and are left together. in a line to mark how far it ranged. But the largest pebbles on the surface of the shore are not only exposed to the upward stroke of the wave. They are also exposed to the onward stroke of the oblique wave. The largest pebbles travel most quickly to leeward, and between all groins this diminishing of the pebbles from the leeward groin to the windward groin may be seen. Now, as the oblique wave travels along shore, but returns straight, there must be a constant passage of water along shore to leeward. This must be compensated by an under current in the sea, and though this under current would not carry shingle, it would carry those finest particles of sand which may be held in suspension, and I think that this is the cause of the accumulation of sand fine enough to blow which is so common at the windward end of large beaches, and which may be observed at Bridport (Bride-port), the windward end of the Chesil beach, notwithstand |