Certain constructions, called "Earth Bridges" (Dobashi), consist of bundles of faggots or small logs laid across a timber frame-work, and covered with about six inches of earth and gravel; both edges are planted with a strip of turf bound with bamboo and cord, to prevent the loose earth from falling away. Bridges of this kind are provided with no hand-rail. Another kind is built of triangular heaps of logs supported underneath by leaning timbers presenting the outline of a pointed arch below, the top surface being covered with earth. Such structures are named "Genkai Bridges," after the Genkai Straits, and are used when the soil of the banks is so hard that it will not allow of piling being driven in.
