1890.] NEW YORK ACADEMY OF SCIENCES, 15 



were no loose blocks, and if these had been formed by erosion 

 alone it was there that we should have found them most numer- 

 ous. 



I had often noticed the gnarled and stunted appearance of 

 the bushes and trees that grew near the shore, and where there 

 was evidently a severe struggle between the sea on the one hand 

 and the plants on the other. 



At Quarantine Station I was shown a small bush, RhacicalUs 

 rtipestris, and was told that it was over twenty-two years old, by 

 a man who said he could remember the plant as "long as he 

 could remember anything." I cut away the rock surrounding 

 the bush, and found that its roots proceeded downward a few 

 inches through the solid rock. At the surface the trunk ex- 

 panded so as to form a projecting mass that rested on the 

 rock. The bush was only about eighteen inches in height 

 and evidently stunted by lack of nourishment. I then pulled 

 up a number of shrubs in the vicinity, and found that their 

 roots ran under the hard crust that formed the surface of 

 the rock. Further observation showed that in many places 

 the crust had been lifted and broken by the growth of the 

 roots, and then trees were noticed with the base of their 

 trunks surrounded by slabs of rocks that leaned against them. 

 Finally, when the rock becomes eroded, the roots of trees pene- 

 trate the holes and crevices, and by their growth crack off large 

 fragments that subsequent erosion forms into boulders. And 

 these boulders are found most abundant where the trees are the 

 largest, and hence where the action of their roots is most vig- 

 orous. Hence we may infer that these blocks are formed by 

 erosion and the growth of the roots of the shrubs and trees. 



While at Nassau I noticed on the shore in some places — as 

 near Dix Point — vertical masses of rock that ran in an irregu- 

 larly curving or straight line on the surface. The projections 

 were sometimes about one foot high and two to four inches in 

 width, and containing on their upper edge a number of holes, 

 about half an inch in diameter, that were often shallow and 

 sometimes mere pits, but quite regularly distributed in a single 

 line. These little ridges could sometimes be traced for a dis- 

 tance of fifteen or twenty feet, and had evidently been left stand- 

 ing while the surrounding rook had been eroded. For a long 

 time I was unable to explain their formation. Sometimes the 

 ridges intersected and formed small or large triangles, as the 

 case might be. When I visited the south side of New Provi- 

 dence, I saw growing in the water, in the calcareous mud that 

 there forms the bottom, the Black Mangrove or Salt Bush {Avi- 

 cetiJiia nitida)y and radiating from it, projecting about five or 



