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We have very little to say in regard to estuarine brick-earths; as might readily be anticipated, they are intermediate in character between fluviatile and marine deposits, and approach the one or the other according to position in the estuary. On the whole, they are variable in character, individual beds being thin. The strata frequently contain abundant plant remains (pieces of wood, etc.), and, except in the case of large rivers, are not noted for yielding very good brick-earths. Sometimes, however, the quality of the clays is not bad, as instance the bricks made in Lincolnshire and Northamptonshire from Jurassic Estuarine clays.

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Turning to brick-earths of marine origin, we may say that these constitute by far the largest class of deposits from which bricks are made in this country, and it will be useful to deal with their origin in some detail. If we attentively watch the action of the weather on a friable sea-cliff we notice that large pieces tumble at intervals on to the beach, and in due time these are washed away by the waves, thus encouraging more to fall when the time is ripe. This process of denudation each year takes tens of thousands of tons of sandy clays and the like from the beaches around our islands. Large pieces of rock, too, are detached by the weather, and eventually succumb to wave action. During storms large stones are hurled against the cliffs, and the general effect of this bombardment is to wear them away, and reduce them to powder and sand grains with all possible expedition. No one who has not seen the waves at work at such times can have any idea of their tremendous power of moving blocks of stone many tons in weight. During calm weather the slight movement of the waves on the beach is manufacturing tons and tons of sand. A mass of gravel falls from the cliff; the finer particles are floated away at the earliest opportunity; the angular stones have their rough projections knocked off by striking against each other; and the incessant movement up and down the beach slope reduces the rough stone to a pebble, all the time the particles thus shaved off are taken out to sea for greater or less distances. If the cliffs are of limestone, or similar rock, both chemical and mechanical methods of denudation come into play, and considerable quantities of lime, &c., are taken away by the sea water in suspension and solution. Large quantities of lime are daily added to the sea through the agency of rivers also.