CORAL-REEFS, 181 



raised together by a widely-acting force : so, perhaps, 

 mountain-chains may subside together. Hence, we cannot 

 tell, whether the Caroline and Marshall Archipelagoes, two 

 groups of atolls running in different directions and meeting 

 each other, have been formed by the subsidence of two 

 areas, or of one large area, including two distinct lines of 

 mountains. We have, however, in the southern prolonga- 

 tion of the Mariana Islands, probable evidence of a line of 

 recent elevation having intersected one of recent subsi- 

 dence. A view of the map will show that, generally, there is 

 a tendency to alternation in the parallel areas undergoing 

 opposite kinds of movement ; as if the sinking of one area 

 balanced the rising of another. 



The existence in many parts of the world of high table- 

 land, proves that large surfaces have been upraised in mass 

 to considerable heights above the level of the ocean ; 

 although the highest points in almost every country con- 

 sist of upturned strata, or erupted matter : and from the 

 immense spaces scattered with atolls, which indicate that 

 land originally existed there, although not one pinnacle 

 now remains above the level of the sea, we may conclude 

 that wide areas have subsided to an amount, sufficient to 

 bury not only any formerly existing table-land, but even the 

 heights formed by fractured strata, and erupted matter. 

 The effects produced on the land by the later elevatory 

 movements, namely, successively rising cliffs, lines of 

 erosion, and beds of littoral shells and pebbles, all requiring 

 time for their production, prove that these movements have 

 been very slow; we can, however, infer this with safety, 



and south line of the Cordillera have been together raised. In the 

 West Indies the N. and S. line of the Eastern Antilles, and the E. 

 and W. line of Jamaica, appear both to have been upraised within the 

 latest geological period. 



