186 



CRETACEOUS ROCKS OF S. INDIA. 



[Part II. § 2. 



they have been formed in situ, hut when washed out and exposed to the 

 action of the air and rain, assume the shining dark-brown surface 

 characteristic of weathered laterite. This form of the soil is very 

 common on the Cuddalore beds in the North-East of Trichinopoly. 



Another form in which the pisiform concretions are so abundant, that 

 when the loose sandy matrix is washed away, they become cemented 

 together as a friable laterite, occurs to the West and North of Vullum in 

 Tanjore, also near Ambapuram (above mentioned), and sometimes on the 

 o-neiss as near Madripet to the North of Oolunderpet, in South Arcot. 



The section at this last place is as follows : — 



Ferruginous sand ... ... ... 3 feet. 



Concretionary lateritic gravel ... 2 feet. 



In this bed the iron was very unequally distributed, some parts being 

 much more closely concretionary than others. 



The sandy soils frequently contain pebbles of gneiss, quartz, &c., 

 sometimes much water-worn, at other times angular and apparently 



Fig. 18. Section of red Sandy Soil in the Velur quarry, near Verdachellum. 



r., Ferruginous sand : r., rolled pebbles : s., Cuddalore Sandstones. 

 just washed up from the surface of the underlying rock. The accom- 

 panying section of the soil resting on Cuddalore sandstones in the 



