ENTRANCE CHANNELS.
247
longitudinal dykes have been resorted to, connected usually with the river
bank by cross dykes. These dykes consist chiefly of earthwork mounds,
protected on the face by rubble or pitching, with a rubble mound on tne
exposed toe ; and occasionally fascines are employed in conjunction with
stoue, or a rubble mound aloue. These régulation works have, for the greater
part, been gradually carried out during the latter half of the nineteenth
century; and two examples of somewhat recent and extensive regulation
works, constructed about half-way between Biebricli and Bingen and just
above Königswinter respectively, are illustrated in ligs. 219, 220. These