DESCRIPTION OF THE PRINCIPAL EXPOSURES. I St) 



Another feature of interest in connection with the charnock- 

 ite series in the Nilgiri Hills is the frequent 

 Schlieren. display of basic schlieren of norites within 



masses of more acid composition, and, what is strictly analogous to 

 this phenomenon, numerous veins of the acid variety running through 

 the basic portions after the manner of the so-called " contemporane- 

 ous veins/' 



According to the relative abundance of the basic and 

 the acid varieties of the same series, we may have, either the 

 basic rock occurring as small islands in an acid matrix, or the latter 

 may occur only as small veins cutting through, and subordinate in 

 quantity to, the former. 



Perhaps the most interesting case is that in which the acid and 

 basic varieties occur together in about equal 



Primary breccia. . . 



proportions, and a very interesting example of 

 such has been exposed on the roadside under the Convent and near 

 the Boat House of the Gymkhana Club in Ootacamund. 



In this pretty instance the basic fragments are scattered 

 through an acid matrix to form a pseudo-breccia; but the linear 

 disposition of the angular, inequiaxed fragments of basic rock, as 

 well as of the acid material in which they lie, indicates the direction 

 of flow previous to consolidation. We have thus a case of what 

 the late G. H. Williams called protoclastic structure in imitation 

 of Lossen's term Primdrtrumer^ and of Sederholm's terms, 

 Primarbreccia and Eruptivbreccia (see fig. 7, and p. 218). 



COORG. 

 The charnockite series occur on the west of Coorg, where 



thev constitute the Western Ghat ridge, and 

 The Western Ghats. 



again on the east, where a large mass, and per- 

 haps several smaller ones grouped around, form lenses, which 

 locally appear as bands, in the biotite gneiss. The direction of foliation 

 is very constantly N.-W. — S.-E. or thereabouts. The former ex- 

 posures run south-eastwards into the Wainad and probably join up with 

 the Nilgiri mass. The eastern margin of these rocks is quartzose and 



( 7i ) 



