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Rh the original labor of construction, added to that of maintenance, makes a total far beyond our comprehension and nearly all of it is the product of human effort.

Fig. 152.— Looking down a steep, narrow Japanese valley at small, flooded and transplanted rice paddies.

The laying out and shaping of so many fields into these level basins brings to the three nations an enormous aggregate annual asset, a large proportion of which western nations are not yet utilizing. The greatest gain comes from the unfailing higher yields made possible by providing an abundance of water through which more plant food can be utilized, thus providing higher average yields. The waters used, coming as they do largely from the uncultivated hills and mountain lands, carrying both dissolved and suspended matters, make positive annual additions of dissolved limestone and plant food elements to the fields which in the aggregate have been very