they are found in metalliferous veins with native
silver and ores of silver, and are usually confined to the upper
oxidized parts of the lodes. They are important ores of silver (the pure
chloride contains 75.3% of silver), and have been extensively mined at
several places in Chile, also in Mexico, and at Broken Hill in New South
Wales. The chloride and chloro-bromide have been found in several
Cornish mines, but never in very large amounts. (L. J. S.)

CERBERUS, in Greek mythology, the dog who guarded the entrance to the
lower world. He allowed all to enter, but seized those who attempted to
escape. According to Hesiod (_Theog._ 311), he was a fifty-headed
monster with a fearful bark, the offspring of Typhon and Echidna. He was
variously represented with one, two or (usually) three heads, often
with the tail of a snake or with snakes growing from his head or twined
round his body. One of the tasks imposed upon Heracles was to fetch
Cerberus from below to the upper world, a favourite subject of ancient
vase-paintings.

CERDIC (d. 534), founder of the West Saxon kingdom, is described as an
ealdorman who in 495 landed with his son Cynric in Hampshire, where he
was attacked at once by the Britons. Nothing more is heard of him until
508, when he defeated the Britons with great slaughter. Strengthened by
fresh arrivals of Saxons, he gained another victory in 519 at
Certicesford, a spot which has been identified with the modern Charford,
and in this year took the title of king. Turning westward, Cerdic
appears to have been defeated by the Britons in 520 at Badbury or Mount
Badon, in Dorset, and in 527 yet another fight with the Britons is
recorded. His last work was the conquest of the Isle of Wight, probably
in the interest of some Jutish allies. All the sovereigns of England,
except Canute, Hardicanute, the two Harolds and William the Conqueror,
are said to be descended from Cerdic.

See _Anglo-Saxon Chronicle_, edited by C. Plummer (Oxford, 1892-1899);
Gildas, _De excidio Britanniae_, edited by Th. Mommsen (Berlin, 1898);
Nennius, _Historia, Brittonum_, edited by Th. Mommsen (Berlin, 1898);
Bede, _Historiae ecclesiasticae gentis Anglorum libri v._, ed. C.
Plummer (Oxford, 1896); E. Guest, _Origines Celticae_ (London, 1883);
J.R. Green, _The Making of England_ (London, 1897).

CERDONIANS, a Gnostic sect, founded by Cerdo, a Syrian, who came to Rome
about 137, but concerning whose histor