100 CRETACEOUS ROCKS OF 8. INDIA. [PaRT II. § 1. 



islands fringed with coral reefs* have an important bearing on 

 this point, and show conclusively that in such localities the tidal 

 and other marine currents frequently bear away for considerable 

 distances sediments composed of the debris of the coral structures 

 intermingled in all proportion with those derived from the neigh- 

 bouring laud. 



We have seen that a large part of the Southern half of the Group is 



nearly unfossiliferous, and such fossils as do occur 

 Fauna of Southern area. ,. i . • 



are for the most part swimmmg or pelagic forms of 



Cephalopoda. The chief exception to the rule are the Inocerami of the 

 beds near Garoodamungalum and Alundanapuram, the little species of 

 oyster which occurs in great abundance in a restricted area to the East 

 of Ootatoor, and the few turbiniform annelids to the East and North- 

 east of the same locality. All these, I can entertain no doubt, are either 

 in situ or have been drifted to a short distance only, seeing that they 

 occur abundantly in particular spots, and there only, and are either un- 

 mino-led with other forms, or are mixed with such forms as are undoubt- 

 edly of swimming and creeping habits, and therefore likely to have 

 reached during life the spot where we now find them imbedded. A mix- 

 ed fauna, resembling that to the North, occurs only at one spot (Muddam), 

 and the coarser nature of some of the beds at this locality, as well as their 

 higher angle of dip, (a point on which I shall enlarge presently,) coincide 

 Avith the fossils in indicating the operation of a local current at this spot. 

 Passing Northwards we have seen that beds of coarse sediment, com- 



^,, ,, posed almost exclusively of srneiss debris, first 



Characters of Northern ^ j a » 



deposits. make their appearance in the upper or latest 



formed beds, and become successively intercalated lower and lower in 

 the series as we proceed further in the same direction ; while bands of 

 limestone gradually increase in number and thickness in the lower 

 part of the formation. Pari passu with this change in the character 

 * See Dana on Coral reefs and Islands, 1853, page 14. 



