My Clarkin branch was based up in Dundee. My grandfather moved down to England in the 1930s and I understand his grandfather was called James (Probably born about 1870). He had about 7/8 children, one of whom I know was called James (Born 1895-ish), but I don't know if that James moved from Dundee (to Glasgow?)or stayed put. Maybe this James was your grandad?
How does this fit in with your family's ages etc.?