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AGASSIZ: THE GREAT BARRIER REEF OF AUSTRALIA. 1 
On our way in and out of Cairns we passed Groen Island, and tho 
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 reof ; 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 
feot 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, rises à few feot above high-water mark, and is 
destitute of vegetation. 
ramble, 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 XIL). Тһе deeper water of the 
channels separating them; from eight to twenty 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," flanked on each side by inner reef flats, more or less widely sepa- 
1 It has been suggested (Kent, Great Barrier Reef, pp. 111, 112, 182) 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 same is the case with the other Queens- 
