elevation and subsidence in the Pacific and Indian Oceans. 309 



ing to the theory recent subsidence, violent earthquakes are known 

 lately to have occurred. 



Theauthor then removedan apparent objection to the theory, name- 

 ly, that subsidence would form a disc of coral but not a cup-shaped 

 mass or lagoon, by showing that the corals which grow in tranquil 

 water are very different from those on the outside, and less effective ; 

 and that as the basin becomes shallower they are subject to various 

 causes of injury. The lagoon nevertheless is constantly filling up to 

 theheight of lowest water spring tides, (the utmost possible limit of 

 living coral,) and in that state it long remains, for no means exist to 

 complete the work. Mr. Darwin then proceeded to the main object 

 of the paper, in showing that as continental elevations act over wide 

 areas, so might we suppose continental subsidences would do, and 

 in conformity to these views, that the Pacific and Indian seas could 

 be divided into symmetrical areas of the two kinds ; the one sink- 

 ing, as deduced from the presence of encircling and barrier reefs, 

 and lagoon islands, and the other rising, as known from uplifted 

 shells and corals, and skirting reefs. The absence of lagoon islands 

 in certain wide tracts, such as in both the West and East Indies, 

 Red Sea, &c, was thus easily explained, for proofs of recent 

 elevation are there abundant. In a like manner, in very many cases 

 where islands are only fringed with reefs, which according to the 

 theory had not been subsiding, actual proofs of elevation were ad- 

 duced. Mr. Darwin remarked that, excepting on the theory of the 

 configuration of reefs being determined by the order of movement, 

 the circumstance that certain classes which are characteristic and 

 universal in some parts of the sea, being never found in others, is 

 quite anomalous, and has never been attempted to be explained. 



Mr. Darwin then pointed out the above areas both in the Pacific 

 and Indian Oceans, and deduced the following as the principal re- 

 sults. 1st. That linear spaces of great extent are undergoing move- 

 ments of an astonishing uniformity, and that the bands of elevation 

 and subsidence alternate. 2. From an extended examination, that 

 the points of eruption all fall on the areas of elevation. The author 

 insisted on the importance of this law, as thus affording some means 

 of speculating, wherever volcanic rocks occur, on the changes of 

 level even during ancient geological periods. 3. That certain coral 

 formations acting as monuments over subsided land, the geogra- 

 phical distribution of organic beings (as consequent on geological 

 changes as laid down by Mr. LyelT) is elucidated, by the discovery 

 of former centres whence the germs could be disseminated. 4. 

 That some degree of light might thus be thrown on the question, 

 whether certain groups of living beings peculiar to small spots are 

 the remnants of a former large population, or a new one springing 

 into existence. Lastly, when beholding more than a hemisphere, 

 divided into symmetrical areas, which within a limited period of time 

 have undergone certain known movements, we obtain some insight 

 into the system by which the crust of the globe is modified during 

 the endless cycle of changes. 



A letter to Charles Lyell,Esq. u On some changes of level which 

 have taken place during the historical period in Denmark" j by G. 



