E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Cyanean Rocks (The).
The Symplegads at the entrance of the Euxine Sea. Said to close together when a vessel attempted to sail between them, and thus crush it to pieces. Cyanan means dark, and Symplegds means dashers together.
Here are those hard rocks of trap, of a greenish-blue, coloured with copper, and hence called the Cyanean.Olivier.