MANUAL or THE NILAGTRI DISTRICT. 



CHAP. V. 



Geology and 

 Mineralogy. 



Iron. 



HomMendic 

 gneiss. 



Mistakes re- 

 garding these 

 rocks. 



Quartz fels- 

 pathic gneiss, 



Quartzo- 



hornblondic 



gneiss. 



They occur '' in short irregular bands or masses in the gneiss, such 

 bands generally running in the direction of the foliation. Haema- 

 tite and specular iron are far more common on the surface than 

 magnetic iron, but from their manner, structure and mode of 

 occurrence, they are probably magnetic iron peroxidized by 

 atmosphei'ic agency.'' Masses of ore occur above the village of 

 Karrashdla, a mile and a half to the west of Kotagiri, and on a 

 spur of the Doddabetta range above the Washermen's — Dhobies' — 

 village at Ootacamand. Similar deposits also occur three miles to 

 the east of Jackatalla or Wellington. Here the haematite is 

 " interfoliated with the gneiss in broad strings of pure mineral." 



In the north-western portion of the Nllagiris the gneiss contains 

 a very large proportion of hornblende, with which is intermixed 

 quartz and some garnets. This rock is described as " a hard, 

 tough, black rock breaking with an even fracture." It contains 

 but few traces of foliation in fresh fractures, but on weathered 

 surfaces it is otherwise. A similar hornblendic gneissose 

 formation constitutes the north-east or lofty section of the 

 Kundas, though here it is stated to be much decomposed, 

 producing " a thick covering of ferruginous clay and lateritic 

 gravel." It is these varieties of gneiss which, Mr. Blandford 

 observes, had misled previous geological observers, who have 

 described them as " syenite, greenstone, and kindred igneous 

 rocks." " Such formations will be seen on the Segore Ghat, 

 where the rock weathers into smooth rounded blocks " without 

 any appearance of foliation- 



Near Sisapara on the Kundas appears another variety of gneissose 

 rock, the component minerals of which are felspar and quartz. 

 This variety was described by Dr. Benza as pegmatite, or graphic 

 granite ; but from the fact that it gradually passes into the 

 neighbouring gneiss, whilst the threads of quartz are " all arranged 

 in the normal direction of foliation," Mr. Blandford does not 

 hesitate to pronounce it a gneissose rock. A similar rock occurs 

 in the valley north-west of Snowdon, and also a more extensive 

 spread north of Melur, " forming a belt about three miles in 

 width passing from the foot of the Kundas to the Kaity valley/' 

 This rock contains also garnets in abundance. 



Mr. Blandford observes that the most common kind of gneiss 

 in the central portions of the plateau is " a finely grained rock 

 composed of quartz, garnet and hornblende, with variable 

 proportions of felspar." Its foliation is indistinct; it is very 

 decomposible, except on the large precipitous faces, and in 

 decomposition forms a large mass of ferruginous clay, embedded 

 in which are large spheroidal boulders. In large exposed faces 



