48 HOLLAND: MICA DEPOSITS OF INDIA. 



pegmatites have been formed from the end-products of the magma 

 whose earlier eruptions produced the " dome-gneiss ". That the " dome- 

 gneiss is foliated, whilst the pegmatites are practically unaffected 

 by earth-movements, does not necessarily imply any great differences 

 in their ages : the amount of deformation suffered by the " dome- 

 gneiss " is no more than might have been brought about during 

 consolidation, and was probably provoked by its own intrusion between 

 the schists ; indeed, it seems likely that the last disturbance of the area 

 was connected with this great granitic eruption, the pegmatitic end- 

 product having found its way as a more mobile, aquo-igneous liquid into 

 the smaller fissures amongst the schists, forming the final phase in 

 the disturbance. 



The schists. — Earlier workers, conforming to the prevalent theory 

 of the time, distinguished the " dome-gneiss " as " metamorphic " and 

 grouped together the associated schists under the term " sub- 

 metamorphic." The peculiar features of the former can all be ex- 

 plained most easily as due to the deformation of igneous intrusions, 

 and the changes are not profound enough to merit the use of the term 

 metamorphic. The scht'sls, however, represent rocks of various 

 origins, which have been made crystalline, and in other respects 

 altered, by the commonly recognised processes of metamorphism. 

 Many, like the hornblende-schists, epidiorites and granulites, differ 

 very little in composition from known igneous types, and probably 

 represent lava flows, intrusive sheets, or even laccolitic intrusions. 

 Others, like the rock near Ga\van containing anthophyllite, retain in 

 places structures which characterise volcanic ashes, whilst the crystalline 

 limestones, quartzites and chiastolite-schists indicate, by their chemical 

 compositions, their origins respectively as limestones, sandstones and 

 shales. These leading types are found in alternating bands of various 

 thickness, representing by their variety the common differences 

 observable in a great sedimentary system, whilst before, during, and 

 possibly since, their metamorphism they have been so profoundly 

 crumpled and folded, that it would be ridiculousto regard the apparent- 

 ly inferior beds to be necessarily older than those resting upon them : 

 ( 38 ) 



