Dictionary of National Biography, 1912 supplement/McMahon, Charles Alexander
McMAHON, CHARLES ALEXANDER (1830–1904), general and geologist, born at Highgate on 23 March 1830, was son of Captain Alexander McMahon of Irish descent, formerly in the Indian service, by his wife Aim, daughter of Major Patrick Mansell (British army). After education at a private school, he obtained a commission in the 39th Madras native infantry on 4 Feb. 1847, but after eight years' service in that regiment became a member of the Madras staff corps, and was transferred in 1856 to the Pimjab commission, on which he served for thirty years, holding the rank of commissioner for the last fourteen. At the outbreak of the Mutiny, McMahon, then a lieutenant and assistant commissioner of the Sialkot district, in which was a cantonment, was in full charge owing to his superior's illness. On 9 July 1857 the native troops rose, and after murdering some Europeans, including four of their officers, decamped to join the rebels. But McMahon contrived to send a note to General John Nicholson [q.v.], who restored order at Sialkot so completely that McMahon was able to force the surrender of some 140 refugee rebels. In 1865 his ability as a judge was proved in a civil suit against the government of India which came before him as a Punjab commissioner. An intricate question, involving about 1,500,000l., had been remitted by the privy council for trial on its merits. McMahon's decision (against the plaintiff) was upheld on appeal by the superior courts of the Punjab and the privy council in England.
While commissioner of Hissar in 1871 McMahon began to work seriously at geology, and six years later published his first important paper in the 'Records of the Geological Survey of India' (vol. x.). This and its successors dealt with a group of crystalline rocks, some of which, after examination with the microscope, he maintained to be eruptive. Subsequently, in 1879, while on a furlough in England, with the rank of lieutenant-colonel, he entered himself as a student at the Royal School of Mines. On returning to India he investigated its rocks with increased vigour, contributing in all twenty-one papers to the 'Records.'
He retired in 1885 with the rank of colonel, becoming major-general in 1888 and lieutenant-general in 1892. Settling in London, he devoted himself to petrological studies, taking part in the proceedings of kindred societies and publishing papers in their journals, the total number of his contributions to geology being nearly fifty. As an investigator he was scrupulously careful and accurate. In petrology he merits a high place among the pioneers, for in 1881 he had 'independently arrived at the conclusion, which then found only a very few supporters in England, that, as a general rule, the extent of metamorphism affords an indication of the relative age of ancient rocks, and in 1884 he maintained, as is now generally admitted, that foliation, in certain crystalline rocks, was due to a flowing of the mass while it was still viscid or partly crystallised. His valuable collection of rock slices was presented by his widow to Manchester University.
He became a fellow of the Geological Society in 1878, and was awarded its Lyell medal in 1899. He was president of the Geologists' Association in 1894-5 and of the geological section at the meeting of the British Association in 1902. In 1898 he was elected F.R.S., and a contribution to the 'Geological Magazine' was published in November 1903. He died at his London house on 21 Feb. 1904.
He was twice married: (1) in 1857 to Elizabeth (d. 1866), daughter of Lieutenant-Colonel Charles Franklin Head, late 93rd highlanders; of his family by her, two sons, the elder being Colonel Sir Arthur Henry McMahon, K.C.I.E., C.S.L, a distinguished officer in the Indian army, who is also a geologist, and one daughter, are still living; (2) in 1868 to Charlotte Emily, daughter of Henry Dorling of Stroud Green House, Croydon, who, with a son and daughter, survived him.
[Proc. Roy. Soc, vol. lxxv.; Geol. Mag. 1904; Quart. Journ. Geol. Soc, 1905; private information; personal knowledge.]