A. E. Verrill— The Bermuda Islands. 483 
differing in fineness and in the amount of small shells and shell-sand. 
It was not very profitable dredging, but the siftings yielded many 
small undescribed shells, annelids, ete. 
On such white bottoms a very large black Holothurian (Stichopus) 
is very abundant. It becomes 15 to 18 inches long, and three or 
four broad. Associated with it are numerous large, nearly black or 
dark purple sea urchins (Zoxopneustes). Both are conspicuous with 
a water-glass, on account of their dark colors. (See Part V.) 
The bottoms of chalky mud make excellent anchorages, for it is 
said that vessels never drag their anchors in it, owing to its tenacity. 
It is related that a British sloop-of-war, the “ Driver,” once lost her 
bowsprit, while weathering a northerly gale in Murray Anchorage, 
by plunging it so deeply under water that she fouled it under her 
anchor cable, but yet did not drag the anchor. 
12.—The Reefs or “ Flats”; North Rocks. 
The outer reefs form an almost continuous semioval boundary wall 
to the region of lagoons, for over 30 miles, from east of St. George’s 
Island all around to and beyond the western end of the group. 
They are from half a mile to two miles or more in breadth and in 
most places are only slightly covered by water at low tide, so that 
the seas break heavily upon them, in long lines of white breakers in 
f. | . 
Figure 27.—The Reefs or Flats near North Rock. Phot. December, 1875, by 
J. B. Heyl. 
windy weather. In many places, as in the vicinity of the North 
Rocks, quite extensive areas of the flat reefs are laid bare by low 
tides. In other large areas the reefs are covered by from 1 foot to 
8 feet of water at low tide. These reefs are very irregular in form, 
