Hi Robin! I have extensive info on John Duthie married to Mary Purvis(I'm of the Purvis branch). A genealogy book was written back in the 40's with this information.
Mary Purvis: Born 3 May 1839 Peebelshire Scotland. Died: 1 May 1877 Emerald Grove, WI Married: 4 April 1861 Janesville, Rock Co. Wi to John Duthie: Born 1834 Kincardinshire SCotland. Died: 23 December 1903 Rockdale Township Hand Co. S. Dakota.
Children: Jane Rentol Alexander C. John Purvis William Millan Mary Susan(Minnie) Elizabeth Purvis Victoria Margaret
I have too much info to put here. Email me your address & I'd be happy to mailyou a copy of what I have!