1857.] Beport on the Progress of the Magnetic Survey. 109 



There exist local accumulations of bivalve shells, constituting 

 neally the whole mass of the rock, for instance at Garudamgalum, 

 near Ootatoor (Trichinopoly district) where the rock is quarried, 

 polished, and sold as "Trichinopoly Marble. 1 ' 



These accumulations may perhaps have been old sea beaches, 

 but they do not constitute a separate or more recent formation 

 than the strata with the ammonites. Close to the accumulations of 

 bivalve shells occur strata containing large ammonites, some of li 

 feet in diameter; and I even saw ammonites in the rock full of 

 the bivalve shells. 



The cretaceous strata seem to have been generally quite undis- 

 turbed ; they repose horizontally upon the oolitic sand-stones at 

 Trivacery and upon the crystalline schists in other localities. 



The cretaceous strata are covered by a deposit of rolled pebbles, 

 with red laterifcic earth, which is evidently more modern and brought 

 down at a former period by violent currents of water from the 

 Eastern Ghauts. 



The deposition of the cretaceous strata took place after the 

 principal upheavemeDt of the Eastern Ghauts, since these strata 

 are nowhere seen to penetrate into the interior of the Ghauts 

 or to the Mysore and Deccan plateaux, and since they have not 

 been affected by the upheaving and disturbing agency, which must 

 have accompanied the formation of the Ghaut Range. 



5. During my visit to the Neilgherries and the Mysore, I was 

 especially anxious to extend my observations in reference to the 

 direction of faults and planes of foliation in the crystalline rocks of 

 Southern India. My observations in various parts of India have 

 convinced me, that the lines of faults and joints and of the direction 

 of the planes of foliation and cleavage, when laid down upon maps, 

 show many very striking coincidences with the main direction of 

 mountain chains and rivers. 



The following are the most important directions of fault and 

 cleavage planes occurring m the Neilgherries and the Mysore 

 plateau : — 



1. Erom N. N. E. to S. S. W., which coincides with the mean 

 direction of the Eastern Ghauts, where the cleavage planes run 

 generally in this direction. 



