100 A. EF. Verrill— The Bermuda Islands; Geology. 
age of the dry land of the Bermudas. At present we can only say 
that this process of accumulation of the red soil is an extremely slow 
one. 
It probably requires the destruction of at least 150 to 200 feet of 
limestone to form one foot of soil, as shown by the chemical analyses 
of the shell-sands and rocks (see pp. 74-75). The amount of 
impurities in the limestone is very small—probably less than an 
average of 0.75 percent. Some of this material in the limestone 
was probably of foreign volcanic origin (floating pumice and ash 
from the West Indian volcanoes perhaps), but some of it may have 
been derived indirectly from the ancient Bermudian voleano. Frag- 
ments of pumice are now rarely found on the shores. Probably the 
amount of this native soil on the island, if evenly distributed over 
the surface, would amount to at least two feet. Though there are 
large tracts where the average depth of soil is not over six inches, 
and also trasts of nearly bare rock, there are depressions and valleys 
between the hills where it is many feet deep. This light soil is 
easily washed from the hillsides into the valleys by the heavy rains, 
unless it be closely covered by grass or some other vegetation. On 
the contrary, as there are no brooks or streams of fresh water, com- 
paratively little of it is now carried into the sea and wasted, though 
streams of considerable size probably existed in the time of Greater 
Bermuda. Hence it follows that unless these limestones disintegrate 
with unusual rapidity, it must have taken a very long penne to 
form even one foot of soil. 
This kind of decomposition of the rocks has been going on during 
the whole history of the islands, since the first dry land emerged, 
for we find numerous layers of the same red-clay interstratified 
between all the limestones ; even those of Pliocene age (see p. 74). 
Perhaps the amount still imbedded in the limestone may be 
actually greater than all the surface soils. 
The limestone thus dissolved and carried away from the surface 
by the percolating rain-water, is afterwards partly deposited in the 
pores of the underlying rocks, making them harder and more com- 
pact; a smaller part is deposited in caverns, in the form of stalactites 
and stalagmites; other portions serve to harden the exposed surfaces 
of rocks and the surfaces of fissures, etc. But a large proportion is, 
without doubt, finally carried into the sea, in solution. 
When unsaturated rain-waters or streams find their way into 
fissures or cavities of the rock, or into loose or soft portions, they 
will gradually dissolve away the rock and form caverns, large or 
