DESCRIPTION OP PLATES. 
XIX 
Lieut. Powell ; scale | of an inch to a mile ; not nearly all tho 
small submerged reefs in the lagoon are represented ; the annular 
reef on the southern side is submerged. 
Fig. 10. — Keeling, or Cocos atoll (or lagoon-island), in the Indian 
Ocean ; from the survey by Capt. FitzRoy ; scale ^ of an inch to 
a mile ; the lagoon south of the dotted line is very shallow, and 
is left almost bare at low water ; the part north of the line is 
choked up with irregular reefs. The annular reef on the NAY. 
side is broken, and blends into a shoal sand-bank, on which the 
sea breaks. 
PLATE II. at end of Volume. 
Fig. 1. — Great Chagos Bank, in the Indian Ocean ; taken from the 
survey by Capt. Moresby and Lieut. Powell; scale ^ of an inch 
to a mile (same scale as Hogoleu, in Plate I.) ; the parts which 
are shaded, with the exception of two or three islets on the 
western and northern sides, do not rise to the surface, but are 
submerged from 4 to 10 fathoms ; the banks bounded by the 
dotted lines lie from 15 to 20 fathoms beneath the surface, and 
are formed of sand ; the central space is of mud, and from 30 to 
50 fathoms deep. 
Fig. 2. — A vertical section, on the same scale, in an E. and W. line 
across the Great Chagos Bank, given for the sake of exnibiting 
more clearly its structure. 
Fig. 3. — Menchicoff atoll (or lagoon-island), in the Marshall Archi- 
pelago, northern Pacific Ocean; from Krusenstern’s atlas of the 
Pacific ; originally surveyed by Capt. Hagemeister ; scale —j of an 
inch to a mile ; the depth within the lagoons is unknown. 
Fig. 4. — Mahlos Mahdoo atoll, together with Horsburgh atoll, in 
the Maldiva Archipelago ; from the survey by Capt. Moresby and 
Lieut. Powell ; scale i of an inch to a mile ; the white spaces in 
the middle of the separate small reefs, both on the margin and 
in the middle part, are meant to represent little lagoons ; but it 
was found not possible to distinguish them clearly from the small 
islets, which have been formed on these same small reefs ; many 
of the smaller reefs could not be introduced ; the nautical mark 
(— ) over the figures 250 and 200 between Mahlos Mahdoo and 
Horsburgh atoll and Powell’s Island, signifies that soundings were 
not obtained at these depths. 
