182 CRETACEOUS ROCKS OF 8. INDTA. [pART II. § 2. 



I have stated above that the fluviatile alluvium consists principally of 

 a pale sandy loam, called by the natives masab. Some other forms of 

 deposit are, however, met with in the broad expanse of the Cauvery delta 

 and elsewhere. Thus to the East of Sheally a dark sandy loam is the pre- 

 valent soil, and a bank section of the Vellaur River at Tolum, (North of 

 Chellumbrum,) exposes beds of black mud and peaty matter, apparently 

 a marsh deposit, alternating with beds of sand probably formed by the 

 river. Two sections of this bank at different spots are as follow : — 

 Section 1.^ Total depth 12 feet 

 3 feet of pale sandy alluvium with MeJania spinulosa. 

 5 feet of black mud with Ampullaria globosa, Paludina melano- 



stomtti and Bithinia pulchella. 

 3 to 5 feet white sand. 



Section II. — Total depth 12 feet. 

 3 feet pale sandy alluvium with a few shells. 



3 feet black mud with shells. Bithinia marginata, &c. 

 1 foot alternations of black mud and sand. 



4 feet white sand. 



4 feet bluish black mud, with root-like calcareous concretions 



and shells, viz.^ Bithinia marginata, B. pulchella, and 



Paludina melanostoma. 



A peaty deposit noticed by Messrs. King and Foote is exposed in 



the bed of the river at low water at the base of the above sections, 



and was not uncovered at the time of my visit. 



Tolum is situated at about 4 miles from the sea, and, except during 

 floods, the water is quite brackish, so that mud deposits with fresh water 

 shells must have been formed under different local conditions from those 

 which now obtain. The Ampullaria and Bithinia are characteristic 

 rather of still water such as that of a marsh, than of a river, while 

 Melania spinulosa of the upper bed of sandy loam is more common in 

 rivers than in tanks or other accumulations of still water. 



