E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
is the Saxon mearc; but marsh, a meadow, is the Saxon mersc, anciently written marash, the French marais, and our morass. The other march is the origin of our marquis, the lord of the march. The boundaries between England and Wales, and between England and Scotland, were called marches.
Riding the marchesi.e. beating the bounds of the parish (Scotch).