144 A. EF. Verrill—The Bermuda Islands; Geology. 
mud, that Mr. Agassiz called “marl.” In such localities there are 
comparatively few living organisms, except some small foraminifera, 
though the common sea-urchin ( Zoxopneustes), the black holothurian 
(Stichopus), and various annelids may also flourish in large numbers. 
‘Such bottoms oceur in Harrington Sound, Hamilton ‘Harbor, Great 
Sound, St. George’s Harbor, ete. 
In some cases part of this ooze or mud has probably been washed 
in from the shores by rains, and in that case it comes from the old 
zolian limestones, as Mr. Agassiz claimed. But I am disposed to 
believe that most of it is recent and of the same origin as the coarser 
particles. The rocks and soil here are so porous that there 1s but 
little running water, even during rains. But during heavy storms, 
especially when of some duration, the water over all the sounds 
often becomes milky with this fine ooze that is stirred up from the 
bottom by the wave-motion. It sometimes does not clear up for a 
day or two. At such times great quantities of the fine sediment is 
deposited in those places where the water is most quiet and thus the 
ooze sometimes accumulates very rapidly.* 
The broken condition of the larger part, even of the smaller shells, 
and the finely comminuted mud are probably largely due to the fact 
that the shells, and even the mud in bulk, are the food of various 
marine animals. Indeed, it is probable that most of this sand and 
mud has more than once passed through the digestive organs of the 
mud-dwelling forms of life, and in this way the shells have been 
broken into small fragments or reduced to powder. 
One of the most important species, for this kind of geological 
work, is a large holothurian (Stichopus Mobii),t which occurs in 
great numbers on all the white muddy bottoms. (Figures 37a, 370.) 
* This fine calcareous mud is carried out to sea many miles by the tides and 
currents, for it largely covers the submarine slopes of the Bermuda mountain at 
all depths down to 2475 fathoms, and as far away as 43 miles, according to 
Thomson. He states (‘‘ The Atlantic,” i, p. 289), that the Challenger sounded on 
the slopes of Bermuda at 120, 780, 950, 1820, 2250, and 2475 fathoms, and at all 
these places the bottom material consisted largely of ‘‘ soft, white, calcareous 
mud, evidently produced by the disintegration of the Bermuda reef and of the 
multitude of pteropod shells that sink down from the surface.” 
+ Several other names have been given to this species. The scarcer variety, 
which is yellowish or brownish with large black spots, agrees best with Mébii 
Semper, of the West Indies. It was later named S. xanthomela by Heilprin. 
The abundant black variety was named S. diaboli by Heilprin, but it seems to 
be only a color variety. The name, diaboli, may well be retained to indicate 
the common black form, as a variety. 
