GEOLOGY 175 



land. " The subsidence such materials produce around them 

 will, in time, make a sea if one does not already exist." 



The Andamans are of Tertiary formation, and of similar 

 geological structure to the Arakan Yoma Range, the line of 

 elevation connecting them with which is represented by the 

 Alguada Reef and Preparis Island. (The Cocos are an integral 

 part of the Andamans.) 



Two sedimentary formations have been distinguished up 

 to the present, the one older, the other newer than the serpentine 

 which intrudes in various localities. They have been called 

 the Port Blair and Archipelago series respectively.* 



The former, occurring in the south, consists of fine grey 

 sandstone — the characteristic rock, generally non-calcareous — and 

 beds of conglomerate and limestone as subsidiary members ; 

 red and green jasper also occur ; possibly, however, of an older 

 series than the sandstone in which they crop out. This series 

 seems to be of early Tertiary or later age. 



The second series, — Miocene, or even newer — of which the 

 whole of the islands of the Archipelago are formed, consist 

 typically of soft limestone, of coral and shell-sand, soft calca- 

 reous sandstones, and soft white clay, with occasionally a band 

 of conglomerate, the pebbles of which seem to have been coral. 



The intrusive rocks of the Andamans — similar to those of 

 Manipur and Burma in the north, and the Nicobars to the 

 south, and of later date than the Port Blair series — are of 

 serpentine, often passing into crystalline diorite and gabbro. 



The Archipelago series seem to cover a large area of the 

 Andamans, while the Port Blair formation is restricted to the 

 south. The greater part of Rutland Island is formed of serpen- 

 tine, in which small layers of brown opal have been met with, 

 and which throughout the group seems disseminated with 

 minute crystals of chromium. The Cinques consist of intrusive 

 rocks of serpentine, associated with metamorphosed, indurated, 

 and sedimentary series, mostly calcareous. The rocks of Little 



* Vide paper on the "Geology of the Andamans," by Dr R. D. Oldham, 

 Proceedings, Geological Su7'vey of India, vol. .wiii. 



