124 HOLLAND: GEOLOGY OF THE NEIGHBOURHOOD OF SALEM. 



Form and modeof . m°re prevalent type of the series, form sepa- 

 occurrence. rate an( j comparatively large masses of a 



roughly lenticular shape in the old biotite-gneiss. Several of these 

 masses, standing up as small, but conspicuous, hills, are seen near 

 Salem and in the wide flat valley stretching eastwards towards 

 Ahtur. These are not the result of the irregular pinching out of 

 thick bands ; for the long axes of the lenses, although parallel to one 

 another and to the general foliation of the country, are not in line, 

 but are arranged en echelon. Their lenticular shape is generally 

 well shown by the contours of the hills, and in one case, | mile east- 

 north-east of Karipatti, a small river has cut across the end of a lens 

 exposing its tapering edge in the highly crushed schists. The 

 rocks composing the lenses are generally without signs- of severe 

 crushing and often quite massive, whilst the other gneisses around, 

 particularly at the edges of the lenses, are highly crushed, sometimes 

 to form real " leaf gneisses." 



Some of the rocks described by Lacroix under his b division 

 of the pyroxenic and hornblendicj gneisses i 

 Lacroix's correlation. were p ro bably obtained by Leschenault from 

 these small hills near Salem ; others, however, cannot be found near 

 Salem, but were almost certainly obtained at considerable distances 

 from the town, and have no known connection with the rocks now 

 under description. Lacroix correlates these rocks with the pyroxe- 

 nic gneisses of North Finisterre, which are regarded as young 

 - members of the French survey division $ f . 



Some of the basic lenticular masses are without garnets and 



resemble very exactly the basic hornblendic 



Distribution. schlieren (autoliths) found in the more acid 



Shevaroy mass ; good examples of these rocks occur in the Salem- 



Ahtur valley (Nos. ir 9 a 3 , 11*926, compared with 11-910, 11-911, 



11-917). Others, generally coarser ingrain, contain garnets and 



» Rec, Geol. Surv. t lnd. t Vol. XXIV, p. U5- 

 ( 22 ) 



