72 CRETACEOUS ROCKS OF S. INDIA. [PaRT II. § 1. 



reef rock is in some parts a coral conglomerate or breccia, made up of fragments firmly 

 cemented. * Over much larger areas it is a fine white limestone, as compact as any 

 secondary marble, and homogeneous in texture. It is often free from any traces of 

 organic life, or proofs of an organic origin. Only now and then an embedded shell 

 or some other relic evinces that animals of any kind were hving in the seas. The 

 white limestone breaks with a conchoidal fracture^ a splintery surface, and rings under 

 the hammer. These facts are of gi-eat importance in deciding upon the origin of the 

 older limestone strata. Other portions of the rock of less extent are made of standing 

 corals, with the intervals filled in by reef debris, and the whole cemented solid. The 

 latter variety here mentioned prevails in the inner patches gi'owing in quiet 

 waters. The former kind is common about the outer reefs, since large areas in 

 the coral plantation are mere sand. It is still more abundant, forming the 

 bottom among the inner patches or in the lagoons, where the finer detritus 

 is washed by the sea.""!" 



I extract this passage in extenso, italicising the most important paragraphs ; as it 

 shows more fairly and strikingly than any summary of mine could do, how close 

 is the resemblance between the limestone of Trichinopoly and that of recent reefs. 

 Both the varieties described by Mr. Dana occur in the Trichinopoly formation, the 

 purely clastic rock being, as in the case of recent coral reefs, the most prevalent 

 of the two. The pale yellow and cream colored tints of the Trichinopoly 

 limestone are, as I have mentioned, in gi'eat part due to infiltration, as is 

 evident from its partial occurrence in some of the specimens; and probably also 

 in part to the admixtm*e in very small proportion of foreign sediment derived 

 fi-om gneiss,! but the proportion, as shown by the composition of the speci- 

 mens examined, is extremely small. 



The rude bedded structure which I have noticed in the Cullygoody reef, is also 



noticed by Mr. Dana,§ Mr. Jukes, || and JNIr. Darwin,^ in 



Bedded structure. .1 • j • j.- ^ . i i i r ^ n 1 • ,i 



their descriptions of the shore rock of reefs ; but m the 



observed cases the angle of dip never exceeds 8°, whereas in the case of the Cullygoody 

 limestone it is sometimes as much as 30".** From this description I should infer that 

 the bedded rock in the latter case had been formed under water, where not exposed 

 to any violent breaker action, in which case the angle of slope might be as high or 

 higher than that observed.-j-f 



I might, had it appeared desirable, have quoted many more passages from the 

 works of modern voyagers, to show how closely our lime- 

 stone formation answers to their descriptions of coral 

 rocks, but I think the above will suffice to prove the point. 



* The italics are ruine.— H. F. B. f See also Op. Cit., pp. 11—27. 



% Compare Darwin's description of the rock of Keeling Atol, (" Observations on coral reefs," 

 p. 12,) where parts of the rock are similarly tinted. Also Dana (Op. Cit., p. 31), 

 § Op. Cit, pp. 16—17. II " Voyage of the F!i/," p. 3. t Darwin, Op. Cit., p. 12, 

 ** See ante, p. 64. ft Darwin, " Obserrations on Volcanic Islands," p. 133. 



