I've been looking for definative proof of who John Marsh of Salem, Massachuseetts parents were in England for four years; Essex, Kent, Somerset, Devon, Lancashire ........ So I have definitely researched the Marsh surname. The French family of De Marisco came to Ireland around 1166 and eventually migrated to the Somerset, England area, then up the coast of Wales to Shropshire and eventually around Manchester. There was also a migration to Devon, Cornwall, Wiltshire, and up north to York, Lincolnshire, and Essex. At that time the French were in power in England. So, you will still find the name Marisco in the records. Later, when the Saxons invaded many former Anglicized names were given German names, such as Merche, Mershe, Marshe and eventually Marsh, particularly in Kent, Sussex, and other southern counties. Now, this is the crux of the matter, it wasn't until around the 15th century that people started using last names and a lot of those names were location names; de la Merse, of the marsh ... There are a lot of marshes in England AND Ireland. Which brings to mind a facinating book I read about the Mariscos' and the De Morres families that emmigrated to Ireland: Genealogical Memoir of the Family of Montmorensey, Styled De Marisco or Morres; ancient Lords De Marisco and Montmarisco, in the peerage of England and Ireland - ..., by Hervey Montmorency-Morres, pub. by J.R. Plassan, Paris, 1817. So, you might research the French name Morres also in Ireland.
Another interesting perspective is of the Marsh families in Northern Ireland which were immigrants from Scotland, in the 17th century, as I recall. After the English got control of Northern Ireland they imported Scottish, (mostly Protestant) to work farms, "Plantations" and bring the Protestant religious conversion. Interestingly, my great-grandmother, Marjorie Josephine McMullen was born in Northern Ireland,and was married in Scotland to a man that was also born in Ireland. It's altogether possible that your people were married in Scotland or were Scottish because the Scottish are known to be Presbyterians.
I think it was a very good idea that you check the Passenger Lists coming from Lancaster and that area because many Scots emmigrated from there. (I found the Marisco book on GOOGLE,"Play". It's free.)
Anyone have definitive proof of John Marsh's ancestry?