282 NOTE ON THE LATEEITIC OF OKISSA. 



thoroughly hardened, tlie lower portion requires exposure to give it 



firmness and strength ; when exposed it becomes 

 Effects of exposure. 



cavernous, owing to the washing away of the softer 



portions, and apparently a chemical change takes place, whereby the 

 iron becomes altered from the state of anhydrous peroxide, (and some- 

 times perhaps also of magnetic oxide,) into that of brown or hydrated 

 peroxide. To this chemical change the coherence may perhaps partly 

 be attributed ; much, however, is doubtless due to the mere thorough 

 drying of the clay by the heat of the sun. The rock passes from 



this compact form, by insensible gradations, into 

 " Laterite gravel." 



the gravel like " Laterite" of Balasore and its 



vicinity. 



In the immediate neighbourhood of hills, and sometimes even for a 



_ . , ,. -i J , -4 1 considerable distance from their base, instances 

 Evidence of its detrital ' 



°"°'°- are numerous, in which pebbles and boulders, 



frequently of considerable size, abound in this deposit. Tliere can be 

 no doubt that these are the result of denudation and transportation, and 

 not of partial disintegration of the underlying rock, because apart from 

 their rounded form, w^hich alone is strong evidence, even if not of itself 

 sufficient to prove that they have been rolled by water, the foliation in 

 different boulders does not coincide, and moreover blocks of many dif- 

 ferent varieties of the metamorphic rocks lie side by side. Near hills of 

 quartzose forms of the gneiss, the ferruginous deposit sometimes passes 

 into a grit, consisting of the mere detritus of the hill cemented by iron. 

 But '' Laterite" frequently extends over flats of many square miles in 

 area, and, at a distance from hills, similarly good evidence of the origin 

 of the rock is wanting. 



In some rare cases, the surface of a rock, either gneiss or sandstone, 

 is exposed, the hollows in which are filled by this form of " Laterite." 

 A beautiful illustration of this occurs in the Mahanadi river, nearly 

 opposite thfe village of Sinilibhaud, 3 or 4 miles above Cuttack. On 



