IN THE MYSORE STATE. 9 



secondary phenomenon after the consolidation of the peridotite, we 

 should not expect to find such a homogeneous result, but would, on 

 the contrary probably find a certain amount of segregation of the 

 products into veins, and stages in the alteration processes. Had the 

 rock, on the contrary, crystallized in its present form as a primary 

 rock, we should not expect the magnetite-dust to be distributed as 

 bands through the breunnerite and the matrix alike, suggesting its 

 excretion during the alteration of a previously existing ferro-magne- 

 sian silicate. The true explanation is probably somewhere between 

 these two extremes, and the homogeneity of the resulting rock-mass 

 is probably due to the fact that the water and carbonic acid which 

 effected the change were originally included in, and uniformly dis- 

 tributed in sufficient quantity through, the magma. 



The kind of alteration by which a simple dunite has been changed 

 into this breunnerite-picrolite-talc rock would not be correctly 

 described as secondary. The consolidation of tire rock and its altera- 

 tion were, if the phenomena have been correctly read, continuous, 

 and are thus related to one another in a way similar to that by which 

 a granite mass and its contemporaneous veins are formed — a series 

 of phenomena in which a definite succession is essential, but which 

 are all parts of one geological effort, and in that sense " contem- 

 poraneous/' It is thus important to distinguish between " primary " 

 or "contemporaneous" alteration, due to the action of vapours 

 originally contained in the magma, and the "secondary" changes 

 induced subsequently and unconnected with the processes of consoli- 

 dation. 



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