84 CRETACEOUS ROCKS OF S. INDIA. [PaUT II. § 1. 



this part is fi-equently subject to much variation of fonn in individuab of the same species, it 



is difficult to determine specific characters with any certainty. 



The occurrence of Belemnites in such vast numbers in these clays, and their comparative rari- 



. , ,„ , ., ty in the beds to the Northwards, (which are characterized by 



Abundance of Belemmtee. •' . . 



an abundance of Qaateroijoda and Bivalves,) is quite in accordance 



with the fact of their prevalence in argillaceous deposits in Eui-ope, such as the Lias, Oxford 



clay, and Gault, and indicates a relation between the mineral character of the rock and the 



abundance of Belemnites, one probable cause of which I have endeavored to explain in the 



appended note.* 



The clays are very uniform in character, and show but few indications of bedding, 



except in the nearly horizontal an-angement of the flaky laminae of which they are 



composed, t 



They extend to within about a mile of the limestone ridge above alluded to, and then 



Upper beds East of Oota- assume a shaly structure, and otherwise become altered in character. 



toor- The zig-zag and fibrous structure becomes prevalent, and the beds 



assimie a bright yellow tint. The bedding is not very clearly marked, but appears to dip 



generally a little to the South of East about 10° or 12°. Belemnites and all the fossils 



Inoceramus the only fossil, characteristic of the clays disappear, and the only organic remains 

 are casts of a species of Inoceramus, which in certain localities are 

 extremely abundant. The species is one very characteristic of the Ootatoor Group, and is allied 

 to I. problematicus, D'Orb., of the Craie chloritee. Bjds of the above character are exposedin the 

 nullahs to the West of Garoodamungalum, and continue up to the overlap of the Trichinopoly 

 beds. Where last seen, on the slopa of the drainage ridge to the North-west of the village, theii- 

 dip turns very decidedly to the South-east, the strike conforming here as elsewhere very closely 

 in direction to the out-crop of the Trichinopoly beds. 



To the North of Garoodamungalum, or rather of the drainage ridge between that village 



North of Garoodamungalum and Terany, the character of the whole Ootatoor Group undergoes 

 and Terany. ^ gradual change. The clays which have hitherto almost ex- 



clusively formed the western part of the group become intercalated with sandy beds and 

 shales similar to those above described, while the upper beds become interstratified with 

 coarse sands, gravels, and bands of calcareous grit, which increase gradually to the North- 

 ward, until they predominate throughout the higher half of the group. At the same time 

 the out-crop of the group widens out, and in a distance of 4 miles, viz., between Garoodamun- 

 galum and Kolokaunuttom, increases from about 2 to 4 miles in width, and in 3 miles more, 



Apparent increase in thick- or in the neighbouihood of Shutauure, to not less than 5 miles. The 

 ness ot group. strike of the upper bads stiU, however, conforms very nearly to 



that of the Trichinopoly Group, and as their average dip does not diminish (indeed betweta 



* The abundance of Belemnites in the argillaceous deposits of Ootatoor, as compared with 

 the more sandy beds only a ie\i miles to the North, appears to me to be explained not so much 

 by the probability that these animals preferred muddy sea bottoms as by the slower deposition 

 of the former beds. Supposing the animals to have been equally abundant during life through- 

 out the entii-e area, we should find their remains most densely accumiilated, where, in a given 

 period of time, the smallest mass of sediment had been deposited, and on the other hand they 

 would be most sparsely disseminated where large quantities of sediment had drifted together. 



t At Numbacoorchy the lamination dipped as much as 15°, I rarely noticed it at so high 

 an angle. 



