(British) Army List - for 1842
Page 52 is part of a list of Majors in the Army, showing George was promoted on 23 November 1841 and is currently posted to 99 Foot.
Page 296 notes Geo. Marmaduke REEVES is currently serving in the 99th (Lanarkshire) Regiment of Foot, with the rank of Captain in the regiment since 20 August 1829, where he is the most senior Captain. He additionally has the Army rank of Major since 23 November 1841.