Optimus
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There appears to be about three William Bridger MARSHs in and around the same area of Kent, although born at different times.
This looks to be your one. He states born Marden, Kent and is fairly consistent with his age in 1871-1901 with Alice.
1851 - HO107/1616/240/15
Pattenden Lane, Marden
George MARSH, head mar 49, Lab on turnpike, born Kent, Marden
Hannah MARSH, wife mar 48, born ditto
George MARSH, son 11, House boyy, born ditto
William B MARSH, son 9, Scholar, born Kent, Marden
Edward MARSH, son 6, Scholar, born ditto
Richard MARSH, son 4, born ditto
Ian C