IN THE MYSORE STATE. 7 



for this idea the breunnerite contains shadowy bands of magnetite- 

 dust distributed irregularly, suggesting its formation by excretion 

 from a previously existing ferriferous mineral like olivine. These 

 bands of magnetite-dust pass sometimes across the borders of the 

 breunnerite crystals into the matrix as if both had been formed 

 during the decomposition of the original ferro-magnesian mineral. 

 Had the breunnerite been of primary origin we should expect to 

 find the inclusions zoned, or at least to be distinct from the matrix. 



It seems likely, therefore, that this rock has resulted from the 

 alteration of a ferro-magnesian silicate rock near dunite, that the 

 alteration was effected under conditions which permitted one of the 

 products, breunnerite, to grow freely from definite crystal-centres, 

 excluding the silica liberated during the process to form picrolite, 

 and with the excess forming the more acid silicate, talc. Talcose 

 masses are not uncommonly found in other magnesite areas in South 

 India, but as a rule the silica liberated during the alteration of the 

 olivine-rock to magnesite Is separated in the form of a chalcedony 

 or quartz. 



In the remarkable instance under description, if the analyses 

 are sufficiently representative, we have had a complete meta- 

 morphosis of the original rock to form a mineral aggregate which 

 can be regarded as olivine-rock plus carbonic acid and water. 

 The whole of the products have been retained within the rock-body 

 to form new minerals instead of being separated as vein material or 

 as special local concretions. The action must have occurred under 

 conditions, as already stated, permitting a free translation of the 

 molecules, and but for the evidence of the magnetite dust-bands, 

 one would naturally imagine that the whole of these changes 

 occurred during, and not subsequent to, the consolidation of the 

 rock. Such an idea involves no greater theoretical difficulties than 

 the idea of secondary alteration of an already-formed olivine-rock 

 by the action of carbonic acid and water. 



The use of the term secondary when applied to rock alteration is 

 but relative. The minerals of early consolidation may be attacked 



( 7 ) 



