A. E. Verrill— The Bermuda Islands; Geology. 49 
appear regularly rounded or somewhat conical ; others form more 
or less long ridges. Some are partly bare of vegetation, near the 
shore, and appear whitish in the distance. 
These hills are all ancient sand-dunes, of which the sands are 
mostly consolidated. The height of these dunes is remarkable, con- 
sidering the small extent of the land. Some are now 200 to 268 
feet high. Nevertheless it is certain that the islands have subsided 
at least 80 to 100 feet,—probably more,—since these hills were 
formed. If we add this to the present height, it will be evident that 
they must have been at one time over 350 feet high, allowing noth- 
ing for the great amount of erosion that they have suffered during 
a long period of time, which would doubtless have amounted to 100 
feet or more. 
In modern times the sands have not been observed to drift more 
than 180 feet high,—and very seldom even to 100 feet. Therefore 
it is evident that the hills could not have reached their great height 
under present conditions. It would have required a much larger 
extent of sandy coast line and much more violent gales, unless the 
islands were undergoing a gradual elevation at the same time, which 
was probably the case. 
These calcareous sands are easily and quickly consolidated by the 
percolating rain-water, which contains calcium bicarbonate in solu- 
tion. Therefore, after being once slightly consolidated, they are not 
liable to be much eroded by the winds, though readily attacked by 
the rains. 
These limestones almost everywhere show their wind-drift origin 
by their very irregular lamination and stratification. The layers are 
of unequal hardness and show very abrupt changes in dip in nearly 
every section, whether in the shore cliffs, road-cuts, or in the quarries 
(figs. 1, 4-6; and pl. xxii, figs. 1, 2). Owing to this structure and the 
very unequal hardness of the layers, the erosion of the clifts by the 
sea has brought about some very remarkable and picturesque forms. 
The topography and physiography of the islands have been so fully 
described and illustrated in my former article,* that it will not be 
necessary to dwell upon those features in this place, except as bear- 
ing directly upon geological changes. Many of the broader and 
more open valleys between the hills are probably the original valleys, 
formed when the hills were built up around them by the winds. 
* These Trans., vol. xi, part 2, pp. 464-490; and ‘‘ The Bermuda Islands,” 
pp. 52-78. 
