Sea. See FOUR SEAS. The main or high seas are part of the realm of England, for thereon the Courts of Admiralty have jurisdiction, but they are not subject to the Common Law. The main sea begins at the low-watermark, but between the high-water mark and the low-water mark, where the sea ebbs and flows, the Common Law and Admiralty have, divisum imperium, an alternate jurisdiction, the one upon the water when it is full sea, the other upon the land when it is an ebb. See FORESHORE.
The jurisdiction of the Admiralty within three miles of the low-water mark will be found elaborately discussed in Reg. v. Keyn, (1876) 2 Ex D 63. In that case it was held by a majority of seven judges to six that the Central Criminal Court had no jurisdiction to try for manslaughter the foreign captain of a foreign ship--the Franconia--which, in passing within three miles of the British shore, ran into a British ship and sank her; but this state of the law was soon afterwards altered by the (English) Territorial Waters Jurisdiction Act, 1878 (41 & 42 Vict. c. 73). S. 2 of that Act enacts that any offence committed by a person, whether a British subject or not, within one marine league of the coast, 'although it may have been committed on board or by means of a foreignship,' is an offence within the jurisdiction of the Admiralty. As to jurisdiction of English Admiralty. As to jurisdiction of English Quarter Sessions to try a case of larceny alleged to have been committed in Scottish waters, see R. v. Devon Justices, (1924) 1 KB 503. See TERRITORIAL WATERS.