Hastings' Dictionary of the Bible (1898)
SID'DIM, THE VALE OF. The name is variously interpreted. " The place is mentioned in Scripture only in connection with the battle between Chedorlaomer and the five confederated kings of Sodom and the adjacent cities. The vale is said to have been full of slime-pits. Gen 14:3-10. The "slime" means bitumen, which abounds in the neighborhood of the Dead Sea, and especially at the southern extremity. The site of the vale of Siddim is connected with that of the destroyed cities of the plain.
The theory has long prevailed that these cities were at the southern extremity of the Dead Sea, and were submerged in it. In that event the southern part of the Dead Sea, below the Lisan Peninsula, is taken as their site, and this would correspond with the vale of Siddim; and thus it is indicated upon many maps. Many scholars, however, are now of the opinion that the cities were not at the south end of the sea, but probably at the north end, and hence that the vale of Siddim must be found in that region also.
The sea is not of recent origin, as the theory of the submergence of those cities would indicate, but the lake is only the remains of a larger and more ancient sea. Dr. Merrill, who favors the northern sites for the lost cities, describes a series of singular pits extending across the Shittim plain, which local tradition declares are very old and were used for military purposes. For a more full treatment of these disputed sites see Sodom, Salt Sea, and Zoar.