88 A. ki. Verrill—The Bermuda Islands; Geology. 
sounds and channels (12 to 14 fathoms), unless we admit that they 
have been eroded by the sea since their submergence. Erosion of 
the sea bottom seems not to have occurred here, unless in very 
shallow water, for the bottom is everywhere covered with a thick 
deposit of incoherent shell-sand and fine, white, calcareous mud, which 
is evidently accumulating faster than it can be removed by the sca. 
Where excavations have been made to deepen the inner channels, 
loose shell-sand has been found to be 6 to 8 feet thick, over the 
eolian limestones. Therefore it is probable that all the deeper 
sounds and channels have been very much filled up since the sub- 
sidence of the land. They may have been originally 40 to 50 feet 
deeper than now. But as some are still 12 to 14 fathoms deep, it is 
safe to assert that the islands were at least 80 to 100 feet higher 
than now, when those deeper places were eroded. 
If we wish to trace the present terrestrial conditions downward 
beneath the sea, it will be necessary to first consider such evidences 
as exist in the shallower waters near the shore. These may be 
found in abundance. Only a few will be mentioned here, as 
examples: 
a. Submerged Caverns and Sinks. 
While blasting out the rocks to deepen the channel at Timlin’s 
Narrows in Hamilton Harbor, in 1843, the drills suddenly entered a 
submarine cavern. When gunpowder was exploded in it, the depth 
suddenly increased from 15 feet to 22 feet. This cavern contained 
red clay and stalactites. J. M. Jones states that in deepening the 
channel into Hamilton Harbor, in 1869, a cavern was found at the 
depth of 36 feet below sea-level.* 
“Blue Hole,” on the west side of Castle Harbor, is a submerged 
deep sink, similar to “ Devil’s Hole” on the land. Many other 
similar sinks or deep “holes” exist here, under the sea. Very many 
more have, no doubt, been so entirely filled up with mud that they 
are no longer visible. Some of the abruptly deeper parts of Harring- 
ton Sound are of the same nature, as are also the deeper parts of 
Castle Harbor and Elies Harbor. 
b. Submerged Sounds or eroded Valleys. 
If we go into deeper water, we find several notable areas of water 
from 50 to 70 feet deep, surrounded on ail sides by shallower areas. 
In a few such places the depth reaches 72 to 84 feet, as in a small 
* American Journ. Sci., Ser. 3, vol. iv, p. 415, 1872. 
