Clever thinking Fifer....sounds logical to me at least 
Annie
Thanks Annie, just thinking "outside the box" but only helps if it provides some answers!

Maybe now would be a good time in this thread to put it all together in a timeline?
This one 1871 & address should be checked against census if we have a specific date before census for Robt jnr's navy admission.
Just wondering if you noticed on Robert Mark Jnr admission in 1871 That his mother's name is down as Janet Black 104 Gerard Street. Also anothert relative is an aunt Mrs Rankin 19 Back Berry Street.
Cheers Sue
And this I agree is probably Janet Mark/s jnr and means her parents/brothers were likely working elsewhere. Helpful though since there may be other misheard "Marsh"s.
1861 Scotland census
James Hutton 1798 Hollywood, Dumfries
Mary Hutton(Smith) 1803 Kirkcudbright
James Hutton 1827 Kirkcudbright
Mary Hutton 1845 Kirkcudbright
Janet Marsh(?Marks) 1851 Liverpool Lancashire. Grand Daughter
Yep we need a timeline of
known facts
