AGASSIZ: THE GREAT BARRIER REEF OF AUSTRALIA. Ill 



On our way in and out of Cairns we passed Green Island, and the 

 fine reef off that island, and examined also the weather reef of Trinity 

 Opening. There is no passage between Green Island Reef and Arlington 

 Reef to the eastward, which forms the northern edge of Grafton Passage. 

 On the west side of Green Island there were patches of beach rock on the 

 coral beach, and all along the west side of the extension of the reef 

 negro heads could be seen well to the south, fringing the whole edge of 

 the reef; a few were seen towards the southern end of the island. We 

 skirted along the western edge of the Green Island and Oyster Reef 

 banks. On the summit of the Southern Cay a few bushes grow a few 

 feet above high-water mark (Plate XXXI.). 



Eastern Oyster Cay is composed of coral sand, and is somewhat higher 

 than the Western Cay. Its summit is covered with low scrub. A new 

 sand cay not indicated on the charts, thrown up very probably since the 

 last surveys were made, l-ises a few feet above high-water mark, and is 

 destitute of vegetation. 



Bramble, Green Island, Arlington, and Oyster Reefs are characteristic 

 reef flats, such as exist on the eastern edge of the inner Barrier Reef 

 channel. At low water many parts of them are bare, and at high water 

 their presence is clearly indicated by the discoloration of the water over 

 the extensive areas they occupy (Plate XII.) . The deeper water of the 

 channels separating them, from eight to twent}' fathoms, stands out in 

 marked contrast by its dark blue color, and renders exploration a 

 comparatively easy task. The flanks of these reef flats are covered by 

 extensive patches of reef corals, growing from depths of from seven 

 fathoms either close to low-water mark in favorable localities, or to the 

 edge of the great flats where the belt of negro heads begins, or where 

 the remnants of the disintegrated elevated reef have covered the surface 

 of the flat with masses of broken corals and coral heads, rendering the 

 surface usually unfit for any extended growth of reef corals. 



Trinity Opening, Grafton Passage, and Flora Pass are wide water 

 ways, 1 flanked on each side by inner reef flats, more or less widely sepa- 



1 It has been suggested (Kent, Great Barrier Reef, pp. Ill, 112, 132) that the 

 great openings through the Barrier Reef were opposite the mouths of the principal 

 rivers of Queensland (Trinity Opening, Flinders, Palm, Magnetic, Flora, Grafton 

 Passages, Capricorn and Curtis Channels), and that though now from thirty to eighty 

 miles distant, yet at one time these breaks were close to the mouths of the rivers, 

 and owe their origin to the fresh water and silt brought down by them. The 

 amount of silt brought down by the Barron River is such as to form an extensive 

 flat off Cairns, extending well out toward Cape Grafton, and naturally interfering 

 with the easy access to that harbor, and the 6ame is the case with the other Queens- 



