174 A. E. Verrill— The Bermuda Islands; Geology. 
Four possible causes for such circular pits,* originating, as they 
often do, in or beneath the red-clay soil, appear to me worthy of 
consideration at present: 
A, There may have been living there in ancient times some bur- 
rowing animal that formed the pits, at least in part. The only 
creature that I can suggest as possible is a large burrowing land 
tortoise, like the gopher turtle of Florida. But I do not know that 
the gopher makes its holes so nearly perpendicular or so circular as 
these structures usually are. The sea-turtles scoop out pits, more 
or less circular, in which to deposit their eggs, but they are more 
irregular in size and form, and not so deep, and are made in the 
beach sands. 
B. In ancient times the sands of Bermuda may have been the 
breeding place of some large gregarious sea-birdt+ that excavated its 
nests in the sand, in the form of round and shallow pits, suitable to 
be the starting point of these cavities. Or some such bird may have 
had the habit of “muffling” itself in the sand to remove vermin, 
after the manner of the domestic fowls, which often form shallow 
round pits in this way. 
C. Some tree or other plant may have formerly existed here that 
had a large cylindrical, perhaps tuberous, root, which may have 
formed the initial pit. The rain-water trickling down all around 
such a root might, by its solvent action, after the death of the plant, 
continue the cavity downward in the same cylindrical form, espe- 
cially if the rain-water should wash clay into the cavity as fast as it 
formed. 
The trunk of the common palmetto is usually somewhat swollen 
or bulbous at the underground base, and not unlike some of these 
cavities in size and form, though usually not so cylindrical. But it 
sends off great numbers of tough rootlets, in every direction. Such 
rootlets ought also to have left casts, but I could find no traces of 
them in the structures that I examined.{ But there may have been 
* In the next chapter (p. 178) some account is given of more irregular struc- 
tures in the limestone apparently due to the stumps and roots of cedar and other 
trees. 
+ The considerable percentage of calcium phosphate in all the ancient red 
clays indicates that birds must have been abundant there in prehistoric ages, 
as they were when the islands were first settled. The presence of the salts of 
potassium also imply the existence and decay of abundant vegetation. 
{ Professor W. N. Rice mentioned finding indentations, looking like the casts 
of rootlets, in the bottom of some of the cavities that he examined. The structures 
