THE GEOLOGY OF BERMUDA. 25 
e 
deep and wide gulf. These hollows are simply caves whose roofs have 
been eroded by the mechanical and chemical action of water, until, too 
weak to support themselves, they have caved in. On the walls of 
these unroofed caves beautiful stalactites may be seen half enveloped 
with velvety mosses and feathery ferns—a strangely beautiful combi- 
nation of the adornments of the underworld with those of the world 
of daylight. In other cases the process of erosion has continued still 
further, so that the sides of the cave, as well as the roof, have been 
entirely removed, and nothing is left to mark the site of the former 
eave but a floor of crystalline stalagmite. Near Walsingham on the 
Main Island, and near Mullet Bay on St. Georges, I observed consid- 
erable areas where the coarsely crystalline calcite forming the sur- 
face rock is unquestionably a stalagmite floor—the only memorial of a 
former cave. 
THE *“‘RED EARTH.” 
> 
The so-called “‘ red earth” bears striking testimony to the amount of 
erosion which the islands have undergone. The usual superficial soil 
of the islands is a clayey earth, sometimes of a deep brick-red color, 
sometimes showing various shades intermediate between this deep red 
and the white or cream-color of the underlying rock. The material is 
occasionally somewhat firmly consolidated, but usually quite soft and 
earthy. It varies much in depth, forming deep pockets in some places, 
while in other places the white rocks are bare. It often occurs in 
eracks and cavities in the rocks. Where any considerable thickness of 
the drift-rock is exposed in a section, as at the extensive quarries on 
Ireland Island, one or more layers of the same “‘red earth” may gener- 
ally be observed extending nearly horizontally at intervals through the 
rock. Various unsatisfactory explanations of the origin and nature of 
this “red earth” have been given. Jones formerly believed it to be 
““composed of decayed vegetable matter”;* and this is indeed the 
common opinion of the inhabitants of Bermuda. Nelson conjectured 
that it was largely derived from the excrements of bats and birds. t 
The true explanation of its origin is undoubtedly that given by Thomson, 
as follows: ‘The coral-sand, like the mass of skeletons of surface ani- 
mals accumulated at the bottom of the ocean, does not consist of ecar- 
bonate of lime alone. It contains about 1 per cent. of other inorganic 
* On the Geological Features of the Bermudas: in Proceedings and Transactions of 
the Nova Scotian Institute of Natural Science, Vol. I., Part IV., Art. II., 1867, p. 21. 
+ Dana, Corals and Coral Islands, p. 391. The citation is from a paper on the Baha- 
mas, in Quarterly Journal of the Geological Society of London, 1853. 
