a: 
NATURE 
267 
- detailed account of it until some investigations which we | 
have stili in hand are completed. 
We met at Bermudas with a singular confirmation and 
illustration of our view as to the organic origin of the 
“red clay” of the Atlantic sea-bed. 
The Islands of Bermudas consist exclusively of lime- 
stone, in some places very compact and hard, almost 
crystalline ; more usually soft and crumbling easily when 
first quarried, but hardening on exposure to the air. 
The limestone is very irregular in the direction of its 
dip. In amount, however, the dip seems never to exceed 
30°. The beds are thrown about in a curious way, every 
quarry or road-cutting showing contortions of all kinds 
in the strata and every amount of irregularity consistent 
with uniformly low angle of dip. One would imagine at 
first sight that the islands exhibited, on a small scale, an 
epitome of the geological phenomena of a disturbed 
palzeozoic district. 
Lieut. (now General) Nelson, R.E., at that time a young 
man, stationed at Bermudas, communicated to the Geolo- 
gical Society of London on April 23, 1834, a very valuable 
paper on the geology of Bermudas, which was published 
in the fifth volume of the Transactions of the Society, 
Lieu. Nelson pointed out that the great proportion if 
not the whole of the Rocks of Bermudas are formed 
simply by the blowing up by the wind of the fine cal- 
careous sand the product of the disintegration of the coral, 
shells, serpula-tubes, and the other constituents of the 
Bermudas reefs, that white sand which we found to extend 
at varying depths through a radius of about 20 miles round 
the island. The sand is washed in by the sea; it is then 
caught at certain exposed points by the prevailing winds, 
blown into sand-hills 4o to 50 ft. in height, which slowly 
move along, forming shoreward a glacis at the angle of 
repose of loose sand, on which lamina after lamina is 
deposited, overwhelming a large tract of country with 
its fields, gardens, and cottages, in a comparatively short 
time, and advancing until its progress is stopped by 
an opposing slope of sufficient height, or by the binding 
of the sand by vegetation. On these wind-blown beds of 
lime, aptly called by Lieut. Nelson, Zolian formations, 
which are originally formed at a considerable inclination, 
changes in the direction and force of the wind-floods of 
sub-tropical rain and other transitory and accidental 
Wr. 2-—Roéks of Coral Sand in Bermudas in process of formation, showing Stratification, and the Stumps of Cedars which have been overwhelmed. 
causes produce with great rapidity all the appearances, 
denudation, unconformability, curving, folding, synclinal 
and anticlinal axes, &c., which are produced in real rocks, 
if I may use the expression, by combined aqueous and 
metamorphic action, extending over incalculable periods 
of time. 
Rain-water contains a considerable quantity of free 
carbonic acid. Water thus charged dissolves the lime | 
rapidly, and the solution of bicarbonate of lime percolat- 
ing through the bed, loses a portion of its car-_ 
bonic acid, and deposits a cement of carbonate of 
lime between the particles of the coral sand. This 
process is kept up not only by the surface rain but 
by the water of the sea, which, as we shall see, percolates 
through the porous stones of the islands. As evidence of 
the universality of this process, we have every crack and 
fissure of the rock filled with semi-crystalline stalagmite, 
-and every here and there the rock is hollowed out into 
caves which in some places assume the proportions of 
magnificent caverns with lofty roofs, supported by huge 
stalagmitic columns, and fretted and enriched by curtains 
and fringes of stalactite. 
One very striking thing about Bermudas is the total 
absence of running water. There is not a trace of a 
stream or pool, or even of a ditch. The rain, which often 
falls in great quantities, sinks through the soil at the spot 
where it falls as it might sink through a sieve. The 
islands are perfectly permeable to water horizontally as 
well as vertically, so that below the level of the sea the 
stone is saturated, or filled with salt water. The fresh 
water lakes and wells, of which there are many, are thus 
merely catches of fresh water lying upon the surface of 
salt water, and they are nearly all slightly brackish, and 
those near the sea rise and fall perceptibly with the tide, 
WYVILLE THOMSON 
