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wall. Various moles or piers exist executed by the ancient Romans in this way. In England where volcanic sand cannot be had, it has been discovered that a mixture of certain clays with lime has a similar and more perfect effect, and the mixtures so made are known as Portland or Roman Cement. In Japan large quantities of Puzzolana exist, and lime stone is also found in various localities, but I can learn of no instances where the mixture of the two was ever attempted. The principle of hydraulic cement is, however, known to the Japanese, and a substance which is formed by a mixture of lime and clay is often used by gardeners as a lining for fish ponds, and for other purposes, but the process of mixture is either defective or the materials used are not good, because although the cement hardens under water to some extent, it does not harden sufficiently and it further cracks and falls to pieces when exposed to frost. Though acquainted with the principle therefore the Japanese seem to have been unable to bring it to any practical result. A lime plaster is made which is tolerably efficient, and is formed by mixing lime with boiled seaweed. But in plastering a house the first coat consists of mud, generally procured from the bottom of some sluggish stream, the second coat of the same substance, this time mixed with sand presumably to harden it, and the lime plaster is then put on as the third coat, but so extremely thin that it is merely a veneer to the mud below it.
A curious system of building retaining walls, sea walls, or the face walls for any embankment or cutting, is so general throughout Japan that one is almost led to believe that the people had discovered some peculiar merit in it, although it is patently in contradiction to all our received notions of masonry. It consists of placing stones on one another which on their faces are square or nearly so but which are pyramidal in shape, and come to a point at their back. They rest at their faces on the thin ledge at the front of the stone and are supported at their backs by small stones loosely inserted, und the walls so built have generally a rubble backing about three or four feet thick.
