1890.] NEW YORK ACADEMY OF SCIENCES. 19 



and slightly elevated pieces of land barely above the level of the 

 surrounding ground^, and on these are growing young pines. 

 These facts show that the pines are advancing as fast as the con- 

 ditions admit. Now, we may fairly suppose that within verff 

 recent geological times the atmospheric conditions were practi- 

 cally the same as now, and that the outward growth of the pines 

 is limited by the elevation of the land from the influence of the 

 salt water. Now, had the land once been as high as at present, 

 it is fair to suppose that the pines would have taken possession 

 of the places they now occupy ; and if subsidence was in pro- 

 gress, they would now be being driven back from their vantage 

 ground. And we may also suppose that before the change from 

 elevation to subsidence had taken place, time enough to allow 

 the pines to grow old would have elapsed ; and hence were 

 the island now sinking, or rather had it recently been sink- 

 ing, we should ex[)ect to find on the western shore the pine for- 

 est with an array of old and dying trees facing the sea, and it 

 would not be surprising if some dead pines were found standing 

 in the water. None of tliese appearances are to be found. 



The mangroves, too, point to elevation, for I find recorded in 

 my note books instances of mangroves, far above high-water 

 mark, that were apparently dying, but none were seen in situa- 

 tions that indicated that the water was becoming too deep for 

 them, as would probably be the case if the land had been re- 

 cently sinking. 



These facts have perhaps been treated with too much detail; 

 but when I had been only to Nassau, and had seen the active 

 erosion that was taking place, I was inclined to think that the 

 islands were sinking, and was afterwards forced by the facts 

 given above to alter my conclusion. That most of the cays are 

 being worn away and reduced in size is evident. The vegeta- 

 tion is being driven backward, as indicated by the old and 

 gnarled appearance of the bushes and by the rhizomorphs that 

 remain where the plants once grew. But on the west side of 

 Andros the water is so shallow for a long distance sea«vard that 

 there is practically no erosion of the land by the waves. A lit- 

 tle bank of coral sand and foraminifera raised slightly above 

 the level of the swash is the only evidence of the action of the 

 water. 



Formation of the Cays North of New Providence. 



The position, size, and shape of these larger cays have already 

 been given on page 5. 



Before attempting to explain the manner in which I believe 

 they were formed, 1 will briefly describe the appearance of the 



