THE BUILDING OF AN ISLAND. 8 1 



seems not impossible that the present considerable depths of water in some of 

 the channels may be the result of local depressions, so that, although it would 

 take a preneral rise equal at least to the above-named depth to bring the bot- 

 toms of the present channels above the sea level, it does not follow that the 

 sinking of the land in its entirety by that amount has been necessary to cause 

 the existing separation. 



Some sinking appears, however, highly probable, and we have already 

 found, while discussing in the last chapter the ponds and lagoons of the island, 

 that these present some local evidence for such a movement, which, however, 

 would probably be the last stage only of the larger movement supposed to be 

 revealed by the present distribution of the plants and land shells. 



So far we have seen that the geological history of St. Croix appears to be 

 bound up with the history of the formation of the east and west axis of the 

 West Indies, but there still remains the question: In what relation does this 

 axis stand to the great north and south axis? As the answer to this question 

 involves some wider considerations than any yet taken up in these pages, it is 

 best to leave it over for the next chapter. 



