58 A. E. Verrill—The Bermuda Islands; Geology. 
I hope to demonstrate later that the rocks which I call the ‘ Wals- 
ingham formation,” and refer to the Pliocene period, now rise to the 
height of 60 to 70 feet and probably much more. If we add to this 
100 feet for the later subsidence, those rocks must have formed hills 
at least 160 to 170 feet high in the Pliocene, even if we allow noth- 
ing for solution and denudation. ‘Their interstratified red clays 
indicate a loss of more than 150 feet by solution. So it is probable 
that the islands were much higher and larger, even in the Pliocene, 
than at present. 
It is certain that it took a very long period of time to bring about 
the elevation of the land and to accumulate the vast quantities of 
shell-sand and red clays contained in the hills. But the mere 
mechanical work of heaping up the sand by the wind is of secondary 
significance in this study. It might have gone on very rapidly at 
times if the winds were more violent than now. This may have 
been the case, especially in the time of the Glacial period. 
What is of far greater significance is the enormous lapse of time 
required for the small shells and other small organisms to grow in 
quantities sufficient to build up all this land, with its high hills, in 
addition to the quantities, perhaps equally great, that were washed 
away into deeper water, and also the great bulk that was lost by 
solution to form the red soil of the dry land and the caverns. 
When these considerations are taken into account, it is plain that 
the building up of Greater Bermuda must have required a vast 
period of time. Therefore, we are forced to believe that it had 
attained very much of its growth in the Pliocene or pre-Glacial times, 
and that it had acquired, before the Glacial period, a large flora and 
fauna of its own, of which some portions still exist, though the 
greater part may have been exterminated by the cooler and more 
stormy climate of that period. 
Perhaps all those plants that are now peculiar to Bermuda (only 
about 8 species*) date from the Pliocene or earlier periods. The 
same is probably true of the few land snails peculiar to the islands, 
especially the genus Pecilozonites, found nowhere else, and of 
which several of the species, including the largest, are known only 
as fossils, while others still survive in diminished numbers and 
feebler forms. Certainly they could not now exist in such places 
as small barren islands where they were once abundant.f 
% For lists of these see these Trans., vol. xi, p. 574, and ‘‘ Bermuda Islands,” p, 
162, with figures. 
+ These matters will be more fully discussed in the chapter on paleontology. 
