GEOLOGY OF THE AREA. 27 



fills a shallow valley between two low gneiss ridges, and the actual 

 channel of the river is cut down to the gneiss below. 



At the northern border and also at the southern border well- 

 rounded pebbles of quartz are abundant in this laterite, which is 

 more or less pellety. 



The band is clearly a river deposit. Near Watapalam, on the 

 north side of the gneiss ridge is another band of laterite, which is, 

 curiously enough, on the same level as the Ponnani laterite. Fig. 

 17, PI. VI, is a section from north to south across the ridge. 



The river north of the ridge runs from east to west along its 

 foot and then turns sharply south and flows through a narrow gorge 

 into the Ponnani River. But the main valley north of the gneiss 

 ridge is continued in a north-westerly direction till it opens into the 

 valley of the Tudhakal River. It is nearly certain that the northern 

 river formerly ran in this valley and was then a tributary of the 

 Tudhakal River, and that the gorge is of late date. 



The height of the Ponnani laterite at Mangara and Watapalam is 

 about 250 to 280 feet. Further down the river a few caps are found 

 at this height, and they were probably once continuous. As the river 

 descends, the height of these caps above the bed increases, for their 

 height above the sea remains the same. But there is a lower late- 

 rite, some 15 feet above the river which slopes down to the sea 

 at the same angle as the river bed, and hence is everywhere at the 

 same height above the river. Near Mangara, which is about 280 feet 

 above the sea and 15 feet above the river ) there is only one late- 

 rite level. The lower sheet of laterite, which has presumably been 

 formed by the Ponnani River from the higher sheet, starts from this 

 point. This is shown diagrammatically in Fig. 18, PI. VI. 



a is the sheet of laterite, 280 feet above the sea. At Mangara 

 its height above the river is about 15 feet, and at Pattambi about 

 200 feet b is the laterite which follows the slope of the river at 

 a uniform height of 15 feet above it. The two bands unite near 

 Mangara. 



About 3 miles east of Pandikdd is a spread of valley laterite, or 



( 227 ) 



