78 GEOLOGY OF TMCHINOPOLYj &C. [ChAP. IV. 1. 



low ground between them is also in great part occupied by dense forest, 

 consisting chiefly of thick underwood, which aids in effectually conceal- 

 ing the face of the country. By far the greater part indeed of the area 

 over which these granitoid rocks are spread is covered with thick scrub- 

 jungle, excepting where clearances have been made for agricultural pur- 

 poses. 



The general appearance of the most typical variety of the granitoid 



gneiss, as, for example, that occurring at Tiagar- 

 Lithological texture. 



Droog, is that of a rather porphyritic granite, con- 

 sisting of quartz and whitish and greyish felspar, including imperfect 

 crystals and grains of a reddish or pink felspar. Apparently included 

 masses of an older hornblendic gneiss are very numerous, and occur of 

 all sizes, from that of a walnut upwards to what would appear to be huge 

 boulders of a ton in weight. Included blocks of such very large size are 

 however of very rare occurrence. One of the finest examples was noticed 

 at the village of Kunniyur, 3 mUes north-east of Tiagar. Here the 

 included blocks were observed in great numbers, some being rounded and 



others angular in shape ; the largest measured up- 

 Included masses. 



wards of 4 feet across, and appeared to be deeply 



imbedded below the surface. Although the matrix has the granitic char- 

 acter strongly developed, none of the included fragments showed any 

 signs of having been exposed to great heat. The included blocks consist 

 of a hard, highly hornblendic schist, which seems generally to resist 

 atmospheric influences far better than does the rock in which they are 

 inclosed. Occasionally, however, they appear to have weathered more 

 rapidly, and to have given rise thereby to cavities much resembling pot 

 holes. Good examples of such included masses may be seen to advantage at 



^ . 1 ,. Yellavanasur, in the old mud fort, also at Cunatur 



Quasi-conglomeratic ' ■' 



^®^^' hill, rive miles east-north-east of Tirukovilur, the 



granitoid rocks assume, near to the village of Chittanur, quite a conglo- 

 meratic appearance ; so numerous are the included fragments which in all 

 ( 300 ) 



