Geology of the Nicobars. 209 



higher points of these having appeared first above the level of the 

 sea, and being exposed to the chemical action of the atmosphere, and 

 the mechanical action of the surf, have principally given the materials 

 for the beds of claystone and conglomerate, of which the first is de- 

 posited in almost still water and the other in stronger currents. 



The following section, (Fig. 1, Plate IV,) may be suificient to give 

 you an idea of the geological constitution of Kamorta. 



The spots marked [* * *,] show the underlying Plutonic rocks, 



[////] tne De ^ s °f c l a y* [••••] sandstone and conglomerate, [ ] 



the recent coral formation. This section may also show, that there 

 is no constant line of strike, and no regular stratification at all. 

 Passing from these Islands down to the southern group, or the Great 

 and Little Nicobars, with the smaller Islands adjoining, we meet with 

 a quite different formation ; here we find a very extensive system of 

 alternating sandstone and slaty claystone or marl, deposited on the 

 bottom of the sea in large beds, and quite independent in their 

 origin from the Plutonic rocks above mentioned. The sandstone is 

 very soft ; but we find imbedded in it another sandstone much harder 

 and forming large balls, disposed generally in ridges, like flint nodules 

 in chalk ; the connecting matter of both kinds is carbonate of lime. 

 Kept some time in muriatic acid, they are converted into sand, com- 

 posed of grains of quartz and mica, which have the same size, and 

 the same aspect, both in the hard and the soft stone. Indeed they 

 only differ in their composition by the quantity of lime contained. 

 The claystone likewise contains much lime and is very hard. These 

 beds are lifted up in a regular manner according to the line of strike 

 from SSE. to NNW., which is found almost the same every where 

 from the north point of the Little Nicobar, to the south point of the 

 Great, and I suppose this is also the case on the Island of Kathshall. 

 It is easy to see that this is the direction of the volcanic belt from 

 Sumatra to the Andaman Islands ; the falling of the strata I have 

 found on the Little Nicobars to be nearly from the middle of the 

 Island to both sides, and independent of the inequalities of the sur- 

 face, the inclination is generally very great, and almost perpendi- 

 cular near the line of elevation. The height of the mountains form- 

 ed by these rocks is not inconsiderable. On the Great Nicobars, they 

 reach 2,500 feet, they are covered with a loose soil containing all 



