BLACKROCK, a reef in the mouth of the Mersey, 3 miles NNW of Liverpool. A lighthouse stands on it, a round white tower, built in 1830, at the cost of £35,000, with a revolving minute light, twice bright and once red, 88 feet high; showing also a fixed light at a lower elevation when there is 12 feet water in the channel.

(John Marius Wilson, Imperial Gazetteer of England and Wales (1870-72))