Complex sentence: Rev. John Marius Wilson was a British writer and an editor, most notable for his "Imperial Gazetteer of England and Wales" (published 1870-1872), a substantial topographical dictionary in six volumes.
Split into simpler sentences: Rev. John Marius Wilson was a British writer and an editor, most notable for his gazettes. The "Imperial Gazetteer of England and Wales" (published 1870-1872), was a substantial topographical dictionary in six volumes.