This quotation seems to be from Sir Henry Alexander (20 June 1875 – 7 April 1940), Editor of the Aberdeen Free Press, Lord Provost of Aberdeen 1932-1935, possibly from the SMC's Guide Book to the Cairngorms that he authored. See In Memoriam Cairngorm Club Journal 81 (1940).
The Gazetteer for Scotland has a length of 58km excluding the headwaters above Loch A'an: "River Avon". Gazetteer for Scotland. Retrieved 11 August 2024.