AGASSIZ: THE GREAT BARRIER REEF OF AUSTRALIA. 187 
diagram he gives of an imaginary section of the Great Barrier Reef, and 
which I here reproduce. 
JuxES's SECTION across THE GREAT. BARRIER REEF. 
e d 
а. Sea outside the barrier, generally unfathomable. 
b. "The actual barrier. 
c. Clear channel inside the barrier, generally about 15 or 20 fathoms deep. 
d. Тһе inner reef. 
e. Shoal channel between the inner reef and the shore. 
F. The great buttress of calcareous rock, formed of coral and the detritus of 
corals and shells. 
G. The mainland, formed of granites and other similar rocks. 
It seems strange that Jukes should have given a section across the 
Great Barrier Reef, and have left out the islands which crop out nearly 
all along the coast’ of Queensland between the mainland and the outer 
or inner line of reefs. This would have given his section an entirely 
different aspect, as he would have had, cropping up and connected with 
the line of the mainland, a series of peaks rising from ten to thirty 
fathoms, round which alone, or round the flat bases of islands and peaks 
which had disappeared from erosion or other atmospheric causes, corals 
had grown. Such a section is not an imaginary one, for the channels 
between the outcropping peaks, islands, reefs, or reef flats are covered 
with the telluric detritus derived from the decomposition of the rocks 
forming those islands, or obtained from the slopes of the mainland. 
Such a section would have shown the layer of corals to be compara- 
tively thin, of not more than twelve to fifteen fathoms, and it would 
have shown the great probability that the outer line of reefs, even built 
upon similar bases, once connected with the mainland, had not attained 
a much greater thickness. See sections across the Great Barrier Reef, 
Plates XXXVII. to XLI. That Jukes himself felt his imaginary sec- 
tion and his explanation of it not to be of universal application can be 
proved from his own words.? He says : — 
! Voyage of the “Fly,” Vol. I. p. 338. ? ]bid. 
