In depths beyond the reach of wave motion, and apart from suspension across a submarine gully, which will sooner or later result in a rupture of the cable, the most frequent cause of interruption is seismic or other shifting of the ocean bed, while in shallower waters and near the shore the dragging of anchors or 40 fishing trawls has been mostly responsible.
Since by international agreement the wilful damage of a cable has been constituted a criminal offence, and the cable companies have avoided crossing the fishing banks, or have adopted the wise policy of refunding the value of anchors lost on their cables, the number of such fractures has greatly diminished.
Petroleum refineries, iron-foundries, chemicals, soap-boiling, silk-spinning and the production of ships' fittings, as marine steam boilers, anchors, chains, cables, are the other principal branches of industry.
In navigation he suggested many new contrivances, such as water-tight compartments, floating anchors to lay a ship to in a storm, and dishes that would not upset during a gale; and beginning in 1757 made repeated experiments with oil on stormy waters.
The profits of the trade were enormous; it was said that even the anchors of ships returning from Spain were made of silver (Diod.