The subsidiary titles are: Earl of Zetland (created 1838), Earl of Ronaldshay (1892) and Baron Dundas (1794). The title Earl of Ronaldshay is the courtesy title of the eldest son and heir of the Marquess.
He was elevated to the peerage as BaronDundas of Aske in August 1794, and was also Lord Lieutenant and Vice Admiral of Orkney and Shetland, Councillor of state to the Prince of Wales (later George IV), President of the Society of Scottish Antiquaries and Colonel, North York Militia.
Thomas Dundas followed his father in having an interest in Grangemouth and in the Forth and Clyde Canal, and he would have been aware of the 1789 trials on the canal of Patrick Miller of Dalswinton's double hulled paddle boat powered with a steam engine fitted by William Symington.
Lord Dundas and some of his relatives and friends were on board for the first sailing of the boat on the canal in 1803, but despite the success of the Charlotte Dundas fears of erosion of the banks prevailed, and the trials were ended leaving Symington out-of-pocket.
In Mr Dundas these recommendations were happily combined with great talents and persevering application to business; so that, although he did not resist the temptations to gaiety and dissipation which beset him, he on no occasion allowed the pursuit of pleasure or amusement, to interfere with the due discharge of his professional duties.
Mr Dundas had been restored to his office of treasurer of the navy, immediately on the formation of Mr Pitt’s administration; and on the passing of the East India bill he was also appointed president of the board of control As treasurer of the navy Mr Dundas’ services were in the highest degree beneficial.
Another of Captain Rannie’s daughters was the wife of Mr Baron Cockburn of the Scottish court of exchequer, and mother to the late Henry Cockburn, Esq., one of the lords of session.