Thanks for your help guys, but i am beginning to wonder if the source i got the original death and monument details from was unreliable. I and another of his descendants that i am in contact with him have been searching for his death details at around this time for a while now and have come up with nothing.
I do believe the birth details that Barbara found are correct. His parents were William Neasmith and Margaret McNeiledge. However he married Margaret Murray in glasgow in 1819.
This is the inscription i have
Sacred
to the Memory of
WILLIAM NEASMITH
late Manager of
Chaneyfield Mills
who died this 14th day of January
1842
Aged 46 Years
This Monument is erected by the workers
as a mark of their respect to his just &
humane conduct while amongst them
He was
Beloved by his friends and esteemed by all
I do know that he did die before 1848 because at this time his widowed wife and four of their children immigrated to Australia.
Thanks again for all your help, I'll keep looking.