=The spit, the bar, and the loop.=—The disposition of shore-deposits depends largely on the currents at and near shore. If the coast-line is deeply indented, the littoral current usually fails to follow the reëntrants. In holding its course across the mouth of a small bay, a shore-current usually passes into deeper water. Here its velocity is checked because its motion is communicated to the water beneath it, and a larger amount of water being involved in the motion, the motion of each part is diminished. If sediment was being moved along its bottom before the current was checked, some part of it is dropped when and where the current is slackened. It follows that deposition commonly takes place beneath a littoral current as it crosses the mouth of a bay. The belt of deposition is often narrow, and the result is the construction of a ridge beneath the water in the direction of the current. The current would never build the embankment up to the water-level, but when its surface approaches the level of effective agitation, the waves may begin to work on it, as on a barrier, and may build it up to, and even above, the surface of the water. So long as the end of such an embankment is free, it is a _spit_ (Fig. 315 and Pl. XXI). If the spit be lengthened until it crosses, or nearly crosses, the bay, shutting it off from the open water, it becomes a bar. Bars have shut in lakes (ponds) on the coast of Martha’s Vineyard, Mass. (Fig. 1, Pl. XXII), and lakes and lagoons at numerous points both on the Atlantic and the Pacific coasts (Fig. 2, Pl. XXII, Rodeo lagoon). The same phenomena are to be seen along many lake shores. Bars sometimes tie islands to the mainland (Pl. XXIII, Fig. 1, Nahant, Mass.; Fig. 2, near Biddeford, Me.). The structure of a bar as seen in cross-section is shown in Fig. 316. The construction of a spit has been aptly compared to the construction of a railway embankment across a depression. The material is first carried out from the bordering upland (shallow water) and dumped where the slope to the depression (deep water) begins. The embankment thus begun is extended by the carrying out of new material, which is left at the end of the dump already made. If the bay across which the bar is built receives abundant drainage from the land, the outflow from the bay may be sufficient to prevent the completion of the bar (Fig. 2, Pl. XXII), for when the growth of the spit has sufficiently narrowed the outlet of the bay, the sediment brought to the end of the spit by the littoral current will be swept out beyond the spit by the current setting out from the bay.