FRINGING AND BARRIER REEFS. Al 
width ; and some of the inner patches are of the same extent; but by 
far the larger part of the reef-ground is covered with deep waters, 
mostly blue like the ocean, and as clear and pure. The sloop of war 
Peacock sailed along the west coast of both Viti Lebu and Vanua 
Lebu, within the inner reefs, a distance exceeding 200 miles. The 
island of Tahiti on its northern side presents us with a good illustration 
PART OF NORTH SHORE OF TAHITI. 
of a narrow channel, and at the same time exhibits the usual broken 
or interrupted character of reefs. The outer reef extends half to two- 
thirds of a mile from the shore. Within it, between Papieti and Ma- 
tavai, there is an irregular ship channel, varying from three to twenty 
fathoms in depth. Occasionally it enlarges into harbours; and in 
other parts it is very intricate, though throughout navigable by 
large vessels. The island of Upolu, of the Samoan Group, is bor- 
dered by a reef nearly a mile wide on part of its northern shore; but 
the waters within are too shallow for a canoe at low tide; and there- 
fore, notwithstanding its extent, the reef is rather a fringing than a 
barrier reef. 
The bottom of these channels or lagoons will take its character, 
as regards the material constituting it, either from the reefs, a source 
of calcareous sand and fragment, or from the earthy detritus of the 
island streams. At Upolu the white coral sands of the reefs, (or in 
more general terms the reef debris,) form the bottom; in some places 
11 
