The various Marpleses give rise to some confusion. Well, they confuse me, anyway.
So far, from Grace's Guide and BPM2, I've found the following;
1) Sorby and Turner, which (I think) became Turner and Naylor, then Turner, Naylor and Marples, of Northern Tool Works, Sheffield; trademark I Sorby, the firm lasting until 1967.
2) William Marples and Sons, founded 1828 by William Marples, later of Hibernia Works, trademark 'Shamrock Brand'. In 1892 they acquired the planemaking business of John Moseley and Sons, London. In 1905 they acquired the business of Thomas Ibbotson and Co, Sheffield. The 1938 catalogue is available to view on the Toolemera website (courtesy of AndyT), and lists both absorbed firms as premium brand trademarks. The business was bought by a consortium of C&J Hampton and William Ridgeway in 1962.
3) Joseph Marples - founded about 1865, and still going.
Were the William Marples (Shamrock brand) and Turner, Naylor and Marples (I Sorby brand) operated independently, or controlled by the same Marples family members? Can anybody put dates to the various company foundations and take-overs?