800 The American Geologist. May, 1897 
her this higher elevation eaiue at first or later in the liis- 
tory. 
The time occupied in the u})buiclingof the present Bermuda 
hills could not have been long. It is all (;ontained within the 
Recent period, for the lowest layers of the dunes rest upon a 
beach rock containing Recent shells. For a mass of hills so 
high to be raised by wind action, considerable time is certain- 
ly required, because the grains of sand must first have been 
formed by animals, then prepared by the waves before being 
built into the islands by wind action. But these processes 
would be aided by the recent elevation, for this would bring 
within reach of the waves material that had formerlj^ been 
scattered on the ocean floor. Moreover such elevation would 
furnish a smooth coast line of low level, along which exten- 
sive beaches could easily be built. Under such conditions of 
recent elevation as have been here suggested, dune forma- 
tion must have been rapid, as it certainly was very eflTect- 
ive. 
It is a notable fact that the high hills and the most con- 
tinuous land of the Bermudas exist on the southern side of 
the great area of shoals. Numerous shallows and some rocks 
occur in the other portions of the reef, but the prominent 
sand hills are all on the southern side. This is probably due 
to the fact that the prevailing strong winds are from the 
south. Hence, here the waves furnished more materials, 
which they were also better able to grind up; and the winds 
were also more powerful in the work of driving the beach 
sand upon the land. No doubt, lower dunes, less numerous 
and more scattered, were accumulated on the northern side, 
having since been destroyed, partly by submergence of the 
land, and partly by wave actii»n. That this is so, is shown 
by the remains of wind blown deposits now present in the 
shallows and rocks of the northern side of the reef. That 
these lower hills could easily be planed down by erosion, will 
be apparent to any one who has seen the activity of wave ac- 
tion upon a soft limestone rock exposed to the heav}^ surf of 
the mid-ocean. 
Recent Subsidence. It has been argued that the present 
irregular form of the Bermuda islands is the result of the cor- 
rosive action of the land water, aided b}^ wave attack, the 
