HOLLAND: CHAKNOCKITE SERIES. 



llanks are precipitous cliffs, which give the hills a peculiarly massive 

 appearance, but the valley of the Vania*r, opening out to the north 

 bisects the mass into two main lobes. 



Messrs. King and Foote agreed with Dr. Benza in classi- 

 fying the rocks of the Shevaroys as hornblende-schist. 1 Hornblende 

 is generally a constituent — often a prominent constituent — of the 

 charnockite series represented in these hills, and in the ultra-basic 

 forms well-exposed near the foot of the ghat leading to Yercaud 

 from the Suramangalam side, hornblende is so abundantly in excess 

 of the hypersthene that the rock might be classified from hand speci- 

 mens as an amphibolite. Sometimes small quantities of felspar occur, 

 and so link these rocks with the norites (No. 9M14). 



The main mass of the Shevaroy hills, however, is composed 

 of u intermediate " members of the charnockite series comparatively 

 free from garnets. Determination of the specific gravity of 48 

 specimens taken from different parts of the mass gave an average of 

 277 with closely agreeing results* In the prevalent intermediate 

 variety there occur frequent examples of coarse-grained, acid con* 

 temporaneous veins, as well as basic, fine-grained, hornblendic 

 schlieren ( irgio, 11*91 1, 11*9:7 ). The basic schlieren are some- 

 times broken into irregularly shaped fragments which are cemented 

 by more acid material, thus producing a kind of primary eruptive 

 breccia. The much more recent dislocation-breccia of the so-called 

 " trap-shotten " kind forms bands in several parts of the hills (irgoo). 



Sections taken from the Shevaroy rocks form good illustra- 

 tions as a rule of the tendency which the ferro-magnesian silicates 

 show to gather themselves into groups. Number 9,111, for instance, 

 shows patches as basic as norite mixed with portions as acid as 

 charnockite (compare slides 1,807 anc * 1,398), 



All the rocks of the Shevaroys appear to be well schillerized, 

 the blue quartz and blue-grey felspars being crowded with the'hair-like 

 inclusions described on p. 138, whilst the hypersthenes show the usual 

 brown rods and plates. Microperthitic felspars are found in all speci- 

 mens (Nos. 9,111, 112, 113,692,693,694,695,696). 



1 Mem. Ceol. Surv. lnd., Vol. IV, p. 242. 



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