Chap. VIII.] athitalook group — trichinopoly district. 131 



Details of the Geological Structia-e. 



The Southernmost point at whicli I have met with beds of the Arrialoor group is between 



the villages of Kullure and Koloture, about 2 miles from the bank 

 Southeni extremity. o ,i r, ■, -, -v-r , ^ m . r„, 



ot the Coleroon, due North of Tanjore. They here crop out from 



beneath the alluvium, or rather the thick cotton soil deposit, which extends along the North 

 bank of the river ; and are laid bare in several little nullahs and patches of broken ground. 

 The beds are yellow sandy shales, with occasional calcareous bands, the whole but slightly con- 

 solidated, and dipping about 4° to the Eastward, and therefore away from the gneiss, which is 

 seen in situ in the village of Kullure, Similar beds are met with at several points between 

 Kulhu-e and Arringauland near Shathamuugalum ; they yield several of the characteristic fossils 



of the group, viz., Ammonites of two or three species ; Nautilus 

 Fossils 



Bouchardianus, D'Orbigny, Nautilus rota, n. s., Voluta, Ostrea 



tegulanea, Forbes, Inoceramus, Trigonia, Pecten 5-costatus, Cardium Hillanum, Area 



Trichinopolitensis ? Opis, Pholadoniya, Terebratula biplicata ? and T. arabilis, Torbes, and a 



Spatangus. 



The greater part of the country to the East and North-east of Koloture is thickly covered 



with red soil, aud nothing is seen of the underlying rocks for 

 Sands at KuUagoody. i ., , t^ 7-, 



several miles ; but at Kullagoody, a mile to the North-east of 



Arringaul, a loose pale-grey and yellow sand, unfossiliferous, and such as characterizes a large 



part of the beds to the Northward, is seen in some irrigation wells in tolerably good sections. 



From Shathamungalum past Keelapulure to the Trigonometrical station of Shillagoody little 

 is seen of the Cretaceous rocks, but on the Northej-n slope of the high ground, (which is 

 covered with small outliers of Cuddalore sandstones,) the beds are well exposed in the nullah^ 

 which carry off its drainage. In one of these, about a mile to the South of Mulloor village a 



Lower beds. MuUoor gneiss ^'^^ ^^^^ ^f gneiss, penetrated by granite, protrudes in the 

 '*°^^' middle of the Cretaceous rocks, which dip away from it on all 



sides. It extends about a quarter of a mile up the nullah, in which the Cretaceous rocks 

 beyond are also well exposed. The lowest beds of these are calcareous and somewhat 

 conglomeratic, frequently including small boulders, but there are no regular accumulations of 

 pebbles, such as characterize some of the lower beds of the Trichinopoly group. Fossils are 

 abundant, especially Terebratula, and Echinida of the genera Spatangus ? and Nucleolites. 



The fossiliferous beds are succeeded by a considerable thickness of w^hite sand, and grey 

 White sands and ferruginous ^^"^ ochreous sandy shales, the former exhibiting but little bedded 

 nodules. structure, except that due to their mode of accumulation by cur- 



rents, of which kind of irregular bedding they offer some veiy beautiful examples. Ferrugi- 

 nous concretions and thin tile-like partings are common in these beds, and have apparently at 

 some former period been collected for smelting by the natives, to judge from the piles of slags 

 met with in the neighbourhood. Excellent sections of these sands, with their capping of Cudda- 

 lore sandstones, are seen in the nullah that runs past Paupanchary into the Murdayaur, and 

 also in the upper part of that which passes to the South of Mulloor. They are for the most 

 part unfossiliferous. 



The nullahs in the neighbourhood of Shillagoody and Karapaudy expose beds similar to 

 FossUiferous beds of SiuUa- *^°^® ^^^"^ Mulloor, viz., Calcareous and sandy shales, abounding 

 S'^°^y- in fossils of a great variety of species. Fine specimens of Nau- 



nlus Bou hardianus are especially abundant. 



