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. Now, what becomes of these vast quantities of detritus furnished to the sea? That depends on the shore currents at the particular locality. If there is not much of a current, the larger grains of grit and sand are soon separated from the rest, and fall to the bottom, whilst the clays are taken farther out to sea before being laid down. But, in any case, the reader will readily perceive that marine deposits must of necessity be on a grander scale, and of a much more substantial character, as a rule, than river, lacustrine, or estuarine deposits. By their mode of origin, too, they must be more homogeneous, whilst they are frequently several hundreds of feet in thickness. In their process of deposition they were not influenced by every storm and freshet; nothing short of great earth-movements in process of time, or some other equally grand phenomena, could disturb the even tenour of their existence. How different to the comparatively insignificant strata formed by the other methods alluded to!