20 LAKE : GEOLOGY OF SOUTH MALABAR. 



In the second (Fig. i), almost the whole surface is covered with 

 laterite, both the hills and the valleys. As some of these hills, includ- 

 ing the western cliff, rise to a height of 150 feet, and are covered from 

 base to summit, it appears as if the laterite were at least 150 feet 

 thick. But this is not by any means always the case. 



The hill forming the edge of the great plateau, about four miles 

 east-south-east of Tanur, is covered with laterite from its foot to its 

 highest point. But its top is a very distinct cap with a vertical scarp, 

 and it is from the foot of the cap that the ground begins to slope 

 down to the sea, so that the laterite on the slope does not seem to be 

 continuous with that of the summit. The section exposed in a small 

 raingully on the side of the hill explains the matter (Figs. 6 and 7, 

 PI. III). 



At the bottom of the gully, gneiss appears at two points (a, b, 

 Fig. 6). Remembering that laterite, except when it occurs as a recon- 

 solidated talus, almost always lies nearly level, the section of the hill 

 must be as in Fig. 7. The thickness of laterite is inconsiderable, and 

 the covering of the side of the hill is the remains of a terrace of laterite 

 or is simply talus fallen from above. 



In other similar cases in this region, a close examination gene- 

 rally reveals a narrow belt of gneiss running round the hill and 

 separating the true cap from the laterite of the valley. Further inland 

 the zone of gneiss becomes better defined, and the laterite is divided 

 into two distinct portions, one capping the hills and the other flooring 

 the valleys. This is very well seen on the road from Tirur Station to 

 Malapuram (near the nth milestone from Malapuram) on the east 

 side of the ridge east of Ponmundum of the map (Fig. 8, PI. III). 



If the valley be narrow, there may be no laterite deposited in it, 

 the whole valley may be gneissic and the laterite forms only a cap 

 to the hills. This is the case in the gorge region. But in this region 

 there are some broad valleys, and it is at the bottom of these that the 

 gorge is cut (Fig. 2). The broad valley is then covered with laterite 

 and the gorge cuts through it into the. gneiss; aiid so a river-terrace 

 is formed. 



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