[From History of Caithness]
This Earl occupied a much less important position than his predecessor. He married at Roseneath 22nd September, 1657. Mary, daughter of the Marquis of Argyll, and died at Thurso Castle in 1676 without issue. Having no male heir to succeed him, and being greatly embarrassed in circumstances - his debts were said to exceed a million merks - he sold his estates and title to his principal creditor John Campbell of Glenorchy. Writing at Thurso Castle, 25th August 1661, he fully explains the effect of the civil wars on his mansions: "I can give account of £200,000 scots of loss I sustained by Generals Middleton and Morgan, besides the burning of my houses, which put me in such a condition that I had not a place to settle myself in till I laid out £1000 to repair the house I live in". [Lauderdale Manuscript, British Museum].
There were two dispositions, as they are termed, in favour of Glenorchy, the first dated 10th June 1661, and the second 8th October 1672, conveying all and sundry, the lands, etc. The latter bears that in case of non-redemption, Glenorchy and his heirs shall be holden and obliged to assume, wear, and use the surname of Sinclair and arms of the House of Caithness. There can be no doubt that this clause was inserted at the desire of Glenorchy, to be used as a pretext for the assumption of the titles at a subsequent period. After this transaction the Earl's chief means of support were derived from an annuity of 2,000 merks, which Glenorchy had bound himself to pay him.
After the Stuart Restoration the Earl became a decided royalist, and manifested great zeal in suppressing conventicles, as appears from a minute in the Presbytery records of Caithness, dated Thurso, 4th November 1674. He was a member of the Privy Council, and Lord Lieutenant of his county. At the time of his death he was an elder in the church of Thurso, which has the following minuted 3rd May 1676: - "Mr. Andrew Munro, minister of Thurso, did represent that the Earl of Caithness, being visited with heavy sickness, did earnestly desire that all the Brethren of the Presbytery should remember him in their public and private prayers to God, which desire was cordially entertained".
The Countess of Caithness soon married her kinsman Glenorchy, who was created Earl of Caithness by patent, but his right to the title was challenged by George Sinclair of Keiss, of whom presently as 45th Earl.
This Earl was committed prisoner to Edinburgh Castle for the slaughter of a soldier sent to quarter for deficiency of cess and excise.