﻿Vol. 6 1.] ANNIVERSARY ADDRESS OP THE J'BESIDENT. li 



the Indian Government, involving a sum amounting to above half a 

 million sterling ; for it was upheld on appeal by both the Superior 

 Court in India and the Privy Council at home. 



About the year 1871 McMahon, then Commissioner of Hissar, 

 began to work at petrological questions, his first contribution, ' On 

 the Blaine Group and the Central Gneiss in the Simla Himalayas,' 

 appearing in the ' Records of the Geological Survey of India ' in 1877. 

 It was followed by ' Notes of a Tour between Spiti & Hangrang ' ; 

 and subsequently, in 1879, while on furlough in England, then 

 a Lieut. -Colonel, McMahon, with characteristic thoroughness, 

 entered as a student at the Royal School of Mines, and attended 

 the lectures by Judd, Huxlej', and Warington Smyth. The ex- 

 perience thus acquired was applied, on his return to India, to the 

 thorough study of the crystalline rocks in the Himalayas ; and he 

 added no less than twenty-one papers to the two already published 

 in the ' Survey Records.' About nine of these were petrographical — 

 careful descriptions of rocks from various localities ; but the remainder 

 for the most part dealt with large petrological questions. He was 

 working along the same lines, but quite independently, as a few, to 

 whom at present he was hardly known, in England. In a paper 

 on the Geology of Dalhousie, written about 1882, he states that 

 he has arrived, from his own observations, at the conclusion that, as 

 a rule, the extend of metamorphism affords an indication of the 

 relative age of ancient rocks ; and in a later paper, ' On the Micro- 

 scopic Structure of some Dalhousie Rocks,' published in 1883, he 

 proves the gneiss of that region to be a true eruptive rock, the 

 structure of which is due to fluxional movements and pressure from 

 adjacent rock-masses, at a time when the intrusive magma was 

 still in a viscid or imperfectly-solidified condition. Thus he ob- 

 tained for himself, while working as a pioneer in these great 

 mountain-ranges, a firm hold on more than one important petro- 

 logical principle. 



After thirty-eight years' service he retired, but was promoted to 

 Major-General in 1888 and Lieut.-General in 1892, and he settled 

 down in London to work steadily at his favourite studies, pub- 

 lishing papers in the ' Mineralogical Magazine,' the ' Geological 

 Magazine,' the Proceedings of the Geologists' Association, and the 

 Quarterly Journal of the Geological Society. The more notable in 

 the last were on the crystalline rocks of the Lizard district, where 

 his Indian experience stood him in good stead, and on the phenomena 

 associated with the Dartmoor granites ; but he did not lose touch 



