IN SOUTHERN INDIA. 



285 



<©ut between the base of the Utatur group and the gneiss. 

 These will be referred to again later on. 



The geographical distribution of these rocks is into three 

 principal areas with three or four small outlying patches. 



The principal of these areas, known as the Trichinopoly 

 area, lies between the Coleroon and the Vellaur, and is of very 

 Irregular shape, measuring about 25 miles in extreme length 

 and width. The next, proceeding northward across the 

 alluvial flat of the Vellar, is the Vriddhachalam area, which 

 extends 15 miles from south-south- west to north- north-east 

 with a width of about 5 miles. Owing to extensive deposits 

 -of soil the cretaceous rocks are very poorly seen here. 

 About 25 miles of alluvium, formed by the Graddelam and 

 Panar (Ponniar) rivers, intervenes between the Vriddhachalam 

 &nd Pondicherry cretaceous areas, which latter extends some 12 

 miles north-eastward with a width of about 6 miles. All 

 three sub-divisions occur together only in the Trichinopoly 

 area ; the Vriddhachalam area is entirely occupied by rocks 

 ©f the upper or Arialur group, while the Pondicherry area 

 shows only the uppermost and lowest or Arialur and Utatur 

 groups, the Trichinopoly group being unknown outside of the 

 Trichinopoly area. The rocks of all the groups show many 

 signs of having been deposited in a sea of shallow character, 

 or of which the depth was but very moderate and the old coast 

 line not 'far off. The Trichinopoly group especially shows 

 markedly the littoral characters of deposits accumulated in 

 shallow water. 



The mineral character of the beds composing the lowest or 

 Utatur group, so called after the large village of that name, 

 ,on the old Madras-Trichinopoly road, is chiefly argillaceous, 

 particularly in the southern part, but in the northern part 

 limestones appear among the lower (western) beds, and sand- 

 stone grits and conglomerates among the upper ones which 

 lie on the eastern side of the Utatur area, the general dip of 

 the formations being easterly at very low angles. A note- 



