INTRODUCTION. 10$ 



principality of Wales and include a remarkably complex series of crys- 

 talline rocks, it is hardly safe to assume that rocks from these two 

 districts are in the geological sense *' associated with one another," 

 and from this assumption to draw an analogy between them and the 

 petrologically similar rocks found together, for instance, in some 

 parts of France. It is stated, for example, that the garnetiferous 

 pyroxenic and hornblendic gneisses (which can easily be identified 

 near Salem) show their analogy with those of Finisterre by being 

 associated with anorthite gneisses and cipolins. 1 But the u anor- 

 thite gneiss " was obtained by Leschenault de la Tour near 

 Sithampundi, 36 miles south-south-west of Salem, whilst crystalline 

 limestones of the kind described are well known near Coimbatore, 

 where Leschenault made a considerable stay on three occasions. 

 There are crystalline limestones, however, of a different kind about 

 20 miles from Salem, but none have been found so far actually asso- 

 ciated with the pyroxenic rocks which abound in the immediate 

 neighbourhood of the town itself. It is of course now well known 

 that pyroxenic gneisses are often found in the neighbourhood of calci- 

 phyres and cipolins, and are then often, as I acroix has pointed out, 

 characterised by the presence of scapolite. But whilst these crys- 

 talline limestones so rich in accessory minerals are nearly always 

 associated with the pyroxene-gneisses ( u pyroxene-granulitcs "), the 

 latter are more often — at least in Southern India — found without any 

 crystalline limestones at all, and the neighbourhood of Salem is appar- 

 ently an instance to the point. 



The pyroxenic gneisses (pyroxene-granulites) which occur in 

 the neighbourhood of Salem, and the similar rock forming such large 

 masses, for instance, as the Nilgiri and Shevaroy hills, have always 

 been regarded by the older members of the Geological Survey of 

 India as belonging to the younger (upper) division of the gneisses ; 

 so far the correlation (proposed by Lacroix) with the subdivisions 



1 Fee, Ceil. Surv., i nd., Vol. XXIV, p. 175. 



( 3 ; 



