TRUE VOLCANOES. 363 



to Kcrguelcn's Island (Cook's Island of Desolation), for the 

 first geological account of which we are indebted to the sue- 

 cessful and important expedition of Sir James Koss. In the 

 harbor called by Cook Christmas harbor (lat. 48° 41', long. 

 G9° 2 / ), basaltic lavas, several feet thick, arc found inclosing 

 the fossil trunks of trees; there also is seen the singular and 

 picturesque Arched Hock, a natural passage through a narrow 

 projecting wall of basalt. In the neighborhood arc conical 

 mountains, the highest of which rise to 2GG4 feet, with ex- 

 tinct craters — masses of green-stone and porphyry, traversed 

 by beds of basalt — and amygdalaid with drusy masses of 

 quartz, at Cumberland Bay. The most remarkable of all are 

 the numerous beds of coal, covered with trap-rock (dolerite, as 

 at Meissner in Hessian %), of a thickness of from a few inches 

 to four feet at the outcrop.* 



If we take a general survey of the Indian Ocean, we shall 

 find the northwesterly extremity of the Sunda range in Su- 

 matra, which is curved, carried on through the Nicobars and 

 the Great and Little Andamans ; while the volcanoes of Bar- 

 ren Island, Narcondam, and Cheduba, almost parallel to the 

 coasts of Malacca and Tenasserim, run into the eastern por- 

 tion of the Bay of Bengal. Along the shores of Orissa and 

 Coromandel, the eastern portion of the bay is destitute of isl- 

 ands, the great island of Ceylon bearing, like that of Mada- 

 gascar, more of the character of a continent. Opposite the 

 western shore of the Indian peninsula (the elevated plain of 

 Neilgherry and the coasts of Canara and Malabar) a range of 

 three Archipelagoes, lying in a direction from north to south, 

 and extending from 14° north to 8° south latitude (the Lac- 

 cadives, the Maldives, and the Chagos), is connected by the 

 shallows of Sahia de Malha and Cargados Carajos with the 

 volcanic group of the Mascareignes and Madagascar. The 

 whole of this chain, so far as can be seen, is the work of cor- 

 al polypes — true Atolls, or lagoon-reefs ; in accordance with 

 Darwin's ingenious conjecture that at this part a large extent 

 of the floor of the ocean forms, not an area of upheaval, but 

 an area of subsidence. 



VIII. The South Sea, or Pacific 



If we compare that portion of the earth's surface now cov- 

 ered with water with the aggregate area of the terra firma 



* Sir James Koss, Voyage in the Southern and Antarctic Regions, vol. 

 i., p. 63-82. 



