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, Rhacicallis 
rupestris, and was told that it was over twenty-two years old, by 
aman 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 rock 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- 
cennia nitida), and radiating from it, projecting about five or 
