278 CORAL FORMATIONS. 



one sinking, 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, etc., 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 adduced. 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 results : — ist. That linear spaces of great extent are 

 undergoing movements 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 geographical 

 distribution of organic beings (as consequent on geological 

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

 discovery of former centres, whence the germs could be dis- 

 seminated. 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. 



