Chap. III.] trichinopoly district — crystalline Rocica. 35 



The plain thus included between the hills and the Cauvery is about 



Rocks of plain to South ^^ 0^" ^^ n^^^^s i^^ ^^i^^^h, and, as described by 



^ ' ^' Messrs. King and Foote, consists mainly of 



homblendic gneiss, the East and West foliation of which coincides 



with the bedding of the original unmetamorphosed 

 Direction of foliation. 



rocks, and with the axis of the great folds into 



which these rocks were bent up probably at a period coeval with 



Coincident with the t^^eir metamorphism. It also coincides, as we have 

 principalphysicalfeatures. ^^^^^ ^-^j^ ^^^^ ^^^^^^ physical features of the 



country, the general direction of the Southern escarpment of the hill 

 country, the granitic ridge of Thutchuncoorchy, and the bed of the 

 Cauvery River. 

 Much of the gneiss to the South of the hills is hornblendic 



Hornblende Schist. Se- ^nd highly foliated. This is well seen in the 

 raganoor. neighbourhood of Seraganoor, where we meet with 



the Western extremity of the Cretaceous rocks. The hornblende schist 

 which occurs here is so highly foliated, that its weathered edges frequently 

 present the appearance of fine shales, an appearance the more deceptive 

 when, as is not unfrequently the case, the dip of the folia is at a 

 comparatively low angle. This kind of rock appears to prevail along 

 the Northern limits of the granitic band, and is met with at several places 

 to the Eastward near the Southern boundary of the Cretaceous rocks. Its 

 occurrence is principally of interest, inasmuch as no similar rock has 

 been met with to the Northward, and as being evidently the source of 

 many of the pebbles found in conglomerate beds of the Trichinopoly 

 and Arrialoor formation. 



A few green-stone dykes are found in the neighbourhood of Ootatoor, 



evidently of prior date to the Cretaceous rocks, 

 Dykes at Ootatoor, r ■ . n -, 



but are oi no miportance as a source of the 



material of the latter. 



I have mentioned that at the foot of the Terany Hill, the extreme 



