Why, when speaking of the branded product Plasticine, did [do?] Irish teachers insist on using the Irish word marla? Even that word was, according to Terry Dolan’s Dictionary of Hiberno-English [Gill & Macmillan, Dublin 2004; new ed forthcoming], derived from the English marl.
At least in the nineteenth century, marl was a valuable manure or fertiliser and, on Lough Derg, Mr Head of the Derry Estate introduced a system of dredging it from deep water. Read about it here.