6 POOTE : GEOLOGY OF MADUEA AND TINNEVELLY DISTRICTS. 



enormous numbers of fresh-water mollusca, especially Melanias, they 

 support. 



A number of lagoons occurs along" the coast in both districts, but they 

 Lngoons and back- ^^'^ ^^ ^^ great size nor of much interest. The 

 waters (Kayals). ^^^^ southerly of these is the Kalampalli Taruvai 



which is formed by the belt of coast dunes extending from Manapada 

 up to Tirucheudur. The water of this lagoon becomes highly brackish 

 in the hot weather. The principal group of lagoons is that formed by 

 the Tambraparni river on the seaward edge of its delta. These lagoons 

 which are locally termed "Kayals" silt up as the delta extends 

 eastward and new ones appear to form by the surf throwing up suc- 

 cessive barriers of sand on which the prevailing winds pile up low 

 dunes. The rate of silting up seems to be rather rapid during the 

 present century judging by the greatly diminished size of the lagoons 

 as shown in the Revenue Survey Map when compared with their ap- 

 pearance in the Atlas sheet (No. 80) which shows their dimensions 

 at the time of the original Trigonometrical survey made about the year 

 1828. The water of some of these lagoons is sufficiently saline to be used 

 for brine at several salt works. To the north of the Tambraparni delta 

 are the lagoons of Taruvai Kulam (Thuroovancolum) and Veppilodai 

 ( Vapulaoda) . The lagoons and creeks near the mouth of the Vaippar and 

 to the south of Melmandai (Mailmuntha) have also decreased in size 

 considerably by silting up. Along the Ramnad coast the great tank 

 shown in the map as extending westward from Valimukkam (Vauli- 

 mookum) is really a salt water lagoon which is connected with tlie sea 

 at Valimukkam by a small tidal creek. The great lagoon north of 

 Kilakarai (Keelacurray) is formed by inundations during heavy rains, as is 

 also the lake-like reach of the Vaigai river to the east of Ramnad town. 

 The lagoon on the north side of Rameswaram island is quite brackish. 

 There is considerable similarity in the climates of Madura and 

 Tinnevelly Districts, both being very dry and 



Climates of the Districts. , , , , . «. , i i ^i 



hot and both bemg affected by the same monsoons. 

 Of the two districts Tinnevelly is the drier, as it gets less of the uorth- 

 ( 6 ) 



