1870.] Brief notes on the Geology SfC of Nancowry harbour. 27 



that they are only " petrographically different products of one and 

 the same period of deposition." 



The sandstones and slates of the southern islands are apparently 

 identical with those of the Andaman s which I examined at Port 

 Blair. They both contain fragments of drift wood changed into 

 coal, and impressions of plants resembling Fucoids. As the two sets 

 of rocks have not been seen, and so far as is known, do not occur iu 

 contact, it is impossible to assert anything positively with regard to 

 their mutual relations. 



If they are to be regarded at all belonging to one formation, then 

 local circumstances must have determined the great difference in 

 lithological character which exists between the rocks of the north- 

 ern and southern islands, while at the same time the processes at 

 work during the deposition of the formation produced uniform re- 

 sults at places not only so distant as Port Blair and the great 

 Nicobar, but as Arracan and Java. Mr. Blanford has stat- 

 ed it as his opinion* that the Andaman sandstones, from specimens 

 brought by Mr. S. K. u r z, are identical with those of Arracan. 

 Dr. Hochstetter, (1. cit.) discusses the probability of the 

 Nicobar rocks being the same age as some occurring in Java and 

 Sumatra. 



The terms " older alluvium" and " marl" which have been used 

 by Dr. E i n k, and Dr. Hochstetter respectively, neither 

 accord very closely with the character of the Oamorta and Nancowry 

 rock, according to the generally accepted English system of rock 

 nomenclature. 



The term alluvium can scarcely be applied to rocks of the age 

 of the claystones of Camorta, rocks whose strata are much disturb- 

 ed, occasionally even being nearly vertical. A marl should contain 

 some percentage of lime, the amount of which is disputed. The 

 Camorta rocks, however, rarely contain even a trace of lime. 



The rocks of these islands which determine the character of the 

 soil are — 



1st. — Coral rocks 'all round the coast. 



2nd. — Magnesian claystones with interbedded conglomerates, of 

 which an admirable section shewing a roll in the beds is well seen 



# Report on the vegetation of the Andaman Islands, by Mr. S.Kur z, p. 2. 



