150 



CEYLON PEARL OYSTER REPORT. 



Silica 55 '00 per cent. 



Carbonate of lime . 3 '50 



Phosphate of lime. 2 - 25 ,, 



Ferric oxide. . . 4 - 10 



Alumina 15 - 80 per cent. 



Magnesia 275 



Water and organic matter 16 - G0 



A few heavy minerals, zircon, tourmaline, and kyanite, occur ; but the bulk is made 

 up of a fine impalpable mud, smooth to the feel, with minute grains of quartz. Only 

 a few organisms, one Foraminifer and a small shell fragment, were found in the sample 

 examined. 



Gulp of Manaak. 



South of Palk Bay, and separating it from the Gulf of Manaar, is Adam's Bridge. 

 Rameswaram Island and Manaar Island, which form the two chief links in the chain 

 of islands almost joining Ceylon with Southern India, consist, according to Foote* and 

 Walther,1" of calcareous sandstone. This is continued across the Pamban Strait and 

 forms the "sandstone quay" of the Tonitoray spit on the west and the coastal part 

 of North Ceylon on the east. The smaller islands between Rameswaram and Manaar 

 also show a similar rock, while through the passages separating them are loose 

 drifting sands. The north coast of Rameswaram is fringed by an ancient coral reef, 

 while living reefs are found in shallow water immediately to the north and to the 

 south. 



South of Adam's Bridge, the Gulf of Manaar stretches as a low sloping beach, 

 deepening fairly evenly at the rate of about 1 fathom in two miles to 20 fathoms, 

 where it sinks more rapidly to great depths. Along the west coast the slope of the 

 shore is more rapid, and deep water is reached sooner. At places along the west 

 coast, and also south of Manaar Island, spits of sand stretch across the platform, 

 mainly near the mouths of rivers. They probably result from the detritus brought 

 down by the rivers, and their general trend towards the north-west may be due to 

 the combined flow of the streams and the prevailing inshore currents. 



On the western shores of the Gulf, and in Palk Bay, the rivers form deltas of large 

 size, and similar spits of sand extend near the river mouths towards the north-east. 

 The coasts of India and Ceylon are swept by great marine currents running up or 

 down the coast according to the monsoons, but owing to the longer duration of the 

 south-west monsoon it produces greater effects, and all rivers flowing into the Gulf 

 have a tendency to extend their deltas towards the north.J The sands covering the 

 floor of the- Gulf become coarser on approaching the west, and there can be no doubt 

 that the material has been carried down from the high grounds by rivers and then 

 distributed by currents on the ocean floor. The granulitic rocks of central Ceylon 



* ' Memoirs of Geol. Survey of India ' Geology of the Madura and Tinnevelly Districts, 

 t Petermann's ' Mittheilungen,' Erganzungslieft No. 102, 1891, 

 | Foote, <>p. at, 



