i4« 



HOLLAND: CHARNOCKITE SERIES. 



the specific gravity of a large number of large specimens, we find 

 that these intermediate members of the charnockite series are com- 

 paratively limited in the extent of their variation, and present an 

 average specific gravity of 2*775, seldom being under 2-72 or over 

 284. It is just possible that if we employed larger specimens the 

 range of variation would be still more restricted. 



As an example in illustration of this statement we may take 

 Specific gravity of the the specimens collected by Dr. H. Warth in 



Intermediate group. _ ,, . . . . . . . , 



bouth Arcot during his survey of that district in 

 1893-94. Neglecting the garnetiferous varieties, which are generally 

 greatly crushed and probably have a specific gravity slightly differing 

 from that of the original unaltered rock, 1 we have the following list 

 of specimens from the South Arcot district. 



Registered No. 



Locality. 



Sp. Gr. 



9>8o5 



Top of Perumakal hill 





2*72 



9,813 



Tindivanum . 





273 



9,786 



Kunam village . 





274 



9.792 

 9,785 

 9,791 

 9,800 

 9>78o 

 9.783 

 9,779 

 9,787 

 9,807 



South of Perumbakam hill 



South-west of Karasanur ...... 



North-east of Perumbakam hill . . . . ' . 



South-west of Molasur • . . . . 



Tirvukarai 



South-east of Nemeli 



Tirvukarai ......... 



Near Kunam village • . 



East-south-east of Eraiyanur . # . . 



Average specific gravity 



275 

 277 

 277 

 278 

 278 



279 

 2*80 

 2*82 

 2-84 



2*774 



1 F. Becke has recently drawn attention to the fact that the minerals formed as the result 

 of dynamometamorphism have generally lower molecular volumes than those of the original 

 constituents from which they have been formed by such secondary processes. The dynamo- 

 metamorphosed rocks thus contain the elements in minerals which occupy the smallest 

 possible space. (" Ueber Beziehungen zwischen Dynamometamorphose und Molecularvolu- 

 men ", Neues Jahrb.f. Min.» 1856, 11, p. 182). 



( 30 ) 



