AGASSIZ: THE GREAT BARRIER REEF OF AUSTRALIA. 99 
in a depth of ninety fathoms, sloping rapidly to thirty-five fathoms in a 
distance of about six miles, and very gradually to sixteen fathoms close 
off the Palm Islands. The slope of Magnetic Passage is similar to that of 
the Palm Passage. The triangular cluster of reef patches separating Mag- 
netic and Palm Channels is about fifteen miles by ten (Plate ХХХ). 
The reef gradually narrows north of Palm Passage, so that off the 
North Barnard Islands it is not more than from ten to twelve miles wide, 
the inner edge approaching at the same time the mainland. Off Double 
Point the inner edge of the reef is not more than twelve miles distant. 
From there to Cape Tribulation the inner edge of the reef is nowhere 
more than six to eight miles distant from the nearest headlands, and its 
width varies from six or eight miles to twelve or fifteen. Flora Pass, 
Grafton Passage, and Trinity Opening slope very gradually, the first from 
thirty-five fathoms to the three fathom line in a distance of thirty miles, 
the second from thirty-five fathoms to the ten fathom line in a distance 
of about twenty miles, while in the last the 100 fathom line is only about 
thirty-five miles from the mainland. The soundings in the opening are 
irregular, but from the inner edge of the reef for a distance of fifteen miles 
the slope is gradual from twenty-four fathoms to the three fathom line. 
The northern extremity of Halifax Bay is flanked by the Palm Islands 
(Plate XXX*.) for a distance of over fifteen miles. Опе of the summits 
of Great Palm Island is over 1,800 fect in height. The Palm Islands 
aro outside the ten fathom line; the northernmost island is seven miles 
distant from the mainland, near the southern entrance of the narrow and 
deep Hinchinbrook Channel, which divides the mainland from the large 
island of the same name. Hinchinbrook Island (Plate XXXI.) is moun- 
tainous. More than twenty miles long, its greatest breadth is fully ten 
miles, and several of its peaks are more than 3,000 feet high. As seen 
from the sea, the island seems to consist of a short chain of mountains, 
in every way similar to those of the parallel range on the mainland, 
and to be separated from them by a deep valley. On the northern 
extension of the Hinchinbrook plateau inside the ten fathom line come 
Goold Island, the Brooke and Family Islands, Dunk Island, and the 
South and North Barnards (Plates XXX." XXXI). From there north- 
ward (Plates XXXII. to XXXIV.), with the exception of the Frankland 
Islands, of Fitzroy Islands, the Low Isles, and Snapper Island, there 
are no islands of importance on the long stretch of coast to Cape Trib- 
ulation. But we are now in the midst of a reef region in which the 
patches are more circumscribed, and not only better defined, but also 
better known. 
