30 LAKE: GEOLOGY OF SOUTH MALABAR. 



layer of very hard chocolate-coloured rock containing grains of 

 quartz. This is about 9 inches thick. In some places (a. Fig. 19) 

 there are several layers of this rock in the laterite, and these unite to 

 the south to form one thin bed. The hard band is therefore to a 

 certain extent interbedded with the laterite. To the north of the 

 figure the chocolate band again rises into the section. Further north 

 it breaks up into several smaller bands, and these thin out gradually 

 and disappear, but still more to the north the band again comes into 

 existence. 



Below the thin hard bed is a very soft sandy clay mottled red 

 and white, but weathering to a dull black. Where the chocolate 

 band dies out, the clay and the laterite come into contact with each 

 other and the clay becomes converted into laterite, so that the 

 distinction between the two disappears. When the band comes in 

 again, the upper and lower parts of the section are again distinct as 

 in the figure. 



In the section close to the station the two rocks are distinct 

 without any intervening hard band (Fig. 20, PL VII). 



In the first section, from the way in which the laterite and the 

 chocolate-coloured rock are interbedded, it is clear that both are 

 detrital. But the lower sandy clay shows no trace of bedding, and is 

 just like the sandy clay formed by the decomposition of felspathic 

 gneiss in other parts of Malabar. Yet, when it is not protected by 

 the hard band above it, it becomes laterite and is undistinguishable 

 from the detrital laterite of the upper part of the section. 



In this case therefore we find a bed of laterite, the upper part of 

 which is detrital and the lower probably formed by decomposition in 

 place of the rock below. 



From the mode of distribution of the laterite of the river terraces 

 and valleys, it seems that this laterite must be mainly of fluviatile or 

 pluvial origin. There are, however, many places where it has been 

 formed by decomposition in situ of the rock below. 



This is especially the case with the valley laterite. Between 

 Cherpalcheri and Angddipuram, about a mile north of Tudhakal ferry, 



( 230 ) 



