Lieut.-Gen. C. A. McMalion. 36-5 



and the rate of erosion of the Spiti valley. Returning home on fur- 

 lough, the Lieutenant-Colonel, as he had then become, showed his 

 thoroughness and zeal for knowledge by entering as a student at the 

 Royal School of Mines, where he attended the lectures of Profs. 

 Huxley, Judd, and Warington Smyth. On going back to India he 

 applied himself with increased vigour to the problems which, as we can 

 see from the writings just mentioned, had already engaged his attention,, 

 and the results of his work are embodied in twenty-one papers 

 published in the " Records of the Geological Survey of India." About 

 nine of them are petrographical ; careful descriptions of the micro- 

 scopic structure of various rocks, such as basalts from Bombay and 

 Aden, or traps from Darang, Mandi, and near Dalhousie ; but the- 

 majority are petrological, where the microscope is made subservient to 

 the study of large questions, raised by his work in the mountain 

 region about Dalhousie and Simla. He states in a paper on the 

 geology of the former, published in Vol. XV of the " Records," that he 

 had independently reached the conclusion for which a few English 

 geologists were then (about 1881) contending : that, as a general rule, 

 the extent of metamorphism affords an indication of the relative age 

 of ancient rocks ; the apparent exceptions, so far as he had seen, being 

 due to faulting. In a later paper, ' On the Microscopic Structure of the 

 Dalhousie Rocks/ he advances a step farther, by proving the axial 

 gneiss of the Dhuladhar range to possess the characteristics of an 

 igneous rock, adding that he now felt obliged to substitute the term 

 " gneissose granite " for " granitoid gneiss " and its equivalent " central 

 gneiss." Writing in the seventeenth volume (1884) on the micro- 

 scopic structure of some Himalayan granites and gneissose granites, he 

 shows the foliation in these rocks to be a result of fluxion in a viscid 

 mass which is .being forced through a fissure in older masses. In later- 

 papers he brings additional evidence to support this conclusion, which 

 he expresses more fully in two communications to the "Geological 

 Magazine " for 1887, namely, that foliation and banding in holo- 

 crystalline rocks are often the result of fluxional movement while in a 

 viscid or even partly crystallized state ; a conclusion which he was the 

 first to demonstrate, and one very valuable at that time as a corrective 

 to exaggerated views of the effect of pressure as an agent of 

 metamorphism. 



On returning to England, after thirty-eight years' service, McMahon 

 settled down with his family in Nevern Square, to devote his leisure 

 to his favourite studies. Among its fruits were four papers which 

 appeared in the " Mineralogical Magazine " (one being an important 

 investigation of the microchemical analysis of rock-making minerals), 

 frequent contributions to the " Geological Magazine " and six papers 



