Hello A.P Duncan,
Re the Duncan/Crosthwaith surname,
The Surname Duncan is Scottish,
I don't know if you have access to the 1850 Directory of Dublin, in it your Crosthwaith Ancestor has a good mention.
Thomas Crosthwaith, was a Director of the Bank of Ireland which was founded in 1783, it was at
2 College Green,
Dublin 1,
It only closed about two years ago, but the Business went to the Central Bank of Ireland ,also College Green,
Telephone them for information at 01677680 or e-mail them at:
www.bankofireland.ie and ask about their Archives.
Leland Crosthwaith and sons seemed to have a Business in Chalpleizod, Co Dublin,
Thomas Crosthwaith J,P 9 Fitzwellian St East also with an address in Chapelizod, called Mulberry House, the above seem to be a family.
I have three Duncans mentioned in the 1850 Directory, William, John and James
Regards Catherine