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 XXX. a ). 



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 a .) for a distance of over fifteen miles. One of the summits 

 of Great Palm Island is over 1,800 feet in height. The Palm Islands 

 are 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. a , 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. 



