ON ITS EXTERIOE. VOLCANOES. 371 



picturesque "Arched Kock" is a natural passage through 

 a narrow projection of basaltic rock. There are in the 

 vicinity conical mounts, of which the highest rise to 

 2664 feet, with extinct craters; masses of greenstone 

 and porphyry traversed by dykes of basalt, and amyg- 

 daloid with quartzose drusic cavities, at Cumberland 

 Bay. Most remarkable are the many beds of coal em- 

 bedded in trap-rock (dolerite as at Meissner in Hesse ? ), 

 varying in thickness from a few inches to four feet. ( 505 ) 

 If we cast a general glance over the domain of the 

 Indian Ocean, we see that the extremity of the Sunda 

 range, which in Sumatra has assumed a north-westerly 

 curvature, is prolonged through the Nicobars, the 

 greater and lesser Andamans, and the volcanoes of 

 Barren island, Narcondam and Cheduba, into the eastern 

 part of the Bay of Bengal, in a line almost parallel to 

 the coast of Malacca and Tenasserim. The western part 

 of the Bay of Bengal, along the coasts of Orissa and Co- 

 romandel, is without islands ; Ceylon, like Madagascar, 

 has rather a continental character. On the western side 

 of the great Indian peninsula, over against the range of 

 the Neilgherries and the coasts of Canara and Malabar, 

 the three groups of the Laccadives, Maldives, and Cha- 

 gos, form in a north and south direction a chain of 

 islands from 14 N. to 8 S. latitude connecting itself 

 through the banks of Sahia de Malha and Cargados 

 Carajos with the volcanic group of the Mascareignes and 

 with Madagascar ; they are all, so far as is visible, struc- 

 tures raised by the coral polypes, true atolls or lagoon 

 reefs ; according to Darwin's ingenious conjecture, that 

 we have here a wide space of sea bottom forming an 

 area not of elevation but of subsidence. 



BB 2 



