16 THE GEOLOGY OF BERMUDA. 
of beach-rock, is shown by its steep landward dip to be the landward 
side of a dune, whose seaward slope has been removed by erosion. The 
dip of the laminz of sand on the seaward face of a dune is, of course, 
seaward. If we conceive the seaward face of the dune to be restored, it 
would certainly in some localities extend beyond the narrow shore plat- 
form into the area now covered by the sea. It is evident, then, that the 
drift-rock of these cliffs on the south shore was formed at a time when the 
islands stood at a higher level than at present. It is easy to see the rea- 
son why the exposures of beach-rock should be much more frequent and 
extensive on the south shore than on the north, in the fact of the vastly 
greater erosive action of the sea on the south shore. The south shore 
receives the full dash of the waves of the Atlantic, while the north 
shore is acted upon only by the lighter waves raised in the great lagoon 
between the shore and the north reef. Another proof of subsidence is 
seen in the occurrence of caves with floors of stalagmite below the 
water level, and with stalactites whose tips are immersed in the sea- 
water.* About the year 1870 “submarine blastings were carried on 
at the entrance of Hamilton Harbor, and at a depth of over 6 fathoms 
a cavern was broken into which contained stalactites and red earth.”t 
In the excavations made somewhat later for the lodgment of the im- 
mense floating dock at the Dockyard on Ireland Island, 46 feet below 
the water-level was found a stratum of “red earth,” 2 feet in thickness, 
containing remains of cedar trees. This stratum was underlain by a 
stratum, 4 feet thick, of hard calcareous sand-rock, containing land 
snails. J. Matthew Jones has called attention to the fact that an ele- 
vation equal to the subsidence indicated by the phenomena observed in 
the excavations at the Dockyard would lay bare the whole elliptical 
area inclosed by the outer reef. + 
The series of movements required to account for the main features of 
Bermudian geology seems to be the following: 1. A subsidence, in which 
the original nucleus of the islands disappeared beneath the sea, the 
characteristic atoll form was produced, and the now elevated beach- 
rock was deposited. 2. An elevation, in which the great lagoon and 
the various minor lagoons were converted into dry land, and the vast 
accumulations of wind-blown sand were formed, which now constitute 
the most striking peculiarity of the islands. 3. A subsidence, in which 
* An elegant description of one of these beautiful caverns may be found in Thom- 
son, op. cit., Vol. I., pp. 304, 305. 
t Jones, Recent Observations in the Bermudas: in Nature, Vol. VI., p. 262. 
t Recent Observations in the Bermudas. 
