11(3 CRETACEOUS ROCKS OF S. INDIA. [PaRT II. § 1. 



of the group, about "half way between the two above-mentioned places, and conglomeratic 

 limestones full of pebbles of gneiss, granite, quartz, and the yellow marls of tlie Ootatoor 

 group, are frequently intercalated in the lower beds. The succeeding beds are fine ochreous 

 shales u,nd silts, with occasional bands of limestone, and in-egular masses of loose sand exhibit- 

 ing frequent irregularities of bedding, especially wherever the sands rest on beds of finer 

 texture. In such cases as that exhibited in Plate III., (a nullah section about a mile 

 to the South-east of Alundanapuram,) it would seem that the 

 Irregular bedding. occurrence of these masses of sand marks a sudden change in the 



direction of a marine current, which at the first burst swept away a portion of the sediment 

 bank previously formed ; drifted a quantity of coarse material over the eroded surface, and that 

 then, as it became more equable and gentle in its flow, finer sediments were successively depo- 

 sited, and a new bank similar to the former gradually formed, the laminae only inclined in a 

 different direction. The dip of these sediment layers is sometimes considerable, and I have once 

 or twice observed it as high as 25°. As in the case of the Ootatoor beds the layers are 

 frequently very thin, and as regular as in the most tranquilly formed horizontal deposits. 



On the whole, tha dip of the higher beds to within a mile of Alundanapuram is to the East 

 and North-east. Beyond this it gradually becomes more conform- 

 of*^i5n-mation" about '^Alunda- able to the general strike of the formation, and about E. S. E. 

 napuram. Meanwhile the irregularities of bedding become less frequent, and 



North of Garoodamungalum the bedding conforms regularly to a general N. E.— S. "W. strike. 

 Fossils are not very common to the South of Alundanapuram, and the few met with in limestone 

 baads are chiefly Gasteropoda and Bivalves. 



The nullah North of Alundanapuram exposes a very good section of the lower part of the 

 group, including the limestone bands, which commence at Alun- 

 un anapu . danapuram and form the prominent ridge between that place and 



Garoodamungalum, frequently referred to as one of the best fossiliferous sites in the group. At 

 the base is a thick mass of fine brown sand, which is, however, not well seen here, but is 

 exposed in a little nuUah about half a mile further to the North. Some few calcareous nodules 

 occur in these beds, but their fossil contents consist of little else than a species of Oyster and a 

 email smooth Pecten, allied to P. orbicularis, both in considerable nimibers. Also a small 

 Spondylus, which is one of the commonest fossils of the group, and is apparently identical with 

 a species very common in the Ootatoor beds at Odium. 



! The limestone, which succeeds, consists of several distinct bands, each 6 or 8 feet in thick- 

 Garoodamungalum lime- ^^^ss, and separated by partings of unfossiliferous shales and white 

 etone (aUell marble). sand, the tail of a thick mass of sand and pebbles which occurs to 



the East of Alundanapuram. The limestone well known as " Trichinopoly marble" is a blue 

 fine g-ained rock, in places crowded with fossils, which are not, however, equally distributed 

 throughout, but as is seen in the case of the smaller shells, arranged in lines of drifting, and 

 very unequally accumulated, so that large masses of the rock exhibit no fossils, while others 

 are more than half composed of shells, most of them of a moderate size. The shells are beauti- 

 fully preserved, the fine polish of the Naticas and Cythereas, and the delicate sculpturing of the 



Murices, Fusi, and Volutes being unsurpassed by the best preserv- 

 ro33ils of limeatone. , . „ , „ , . 



ed specimens of recent shells, and m some cases traces even of 



the original coloring are still distinguishable. The number of species is very great, and 



includes Gasteropods and Conchifera in almost equal numbers. Among the most abundant 



ani characteristic of the fonner are Stromhua contortus, Sow., two or three species of 



