AGASSIZ: THE GREAT BARRIER REEF OF AUSTRALIA. 141 
There is nothing to show that the slope of the continental plateau has 
been modified by the growth of the Great Barrier Reef, and that we have 
a steep pitch (almost a vertical rise, due to the growth of corals) from 
unfathomable depths to the edge on the sea-face of the living Great Bar- 
rier Reef, On the contrary, the steopest slope of the continental shelf 
off the Australian continent is in the region south of the Great Barrier 
district. 
On examination of the sections on Plates XXX VII. to XLI., it will be 
seen that they consist of two distinct types. One of these corresponds 
in a general way to the imaginary section given by Jukes ; such as Plate 
XXXVIL Figs. 4, 7; Plate XXXIX. Figs. 13, 15; Plate XL. Figs. 
19, 22. The other type is radically different, and is inconsistent with 
the existence of a coral reef rock extending from the outer barrier reef 
to the shore of the mainland ; it is represented by such sections as Plate 
XXXVILI. Figs. 8-10, Plate XXXIX. Fig. 16, and Plate XL. Figs. 
91, 24, 25, in which islands of considerable height similar in geological 
structure to that of the mainland protrude along the line of the section, 
clearly indicating that the continental slope extends from the mainland 
out to the edge of the Barrier Reef, and is only covered by a limited 
depth of coral reef rock, or by telluric deposits derived from the dis- 
integration of tho rocks on the slopes of the mainland and of the out- 
lying islands. 
In the one case, the sections have been made across a region in which 
the islands once existing off the mainland have been eroded and denuded 
and levelled off into flats, now covered with coral reefs, while in the 
other ease the sections have been made across a district in which the 
islands, while they have undoubtedly been greatly worn, yot remain suf- 
ficiently high to show their former connection with the continental area. 
Perhaps no two sections indicate this contrast more markedly than 
the western section through Torres Strait (Fig. 28 on Plate X LI.) across 
the line of islands and reefs extending from the mainland to New 
Guinea, and the seetion moro to the eastward from Mount Adolphus 
to Dane Road in New Guinea, (Plate XLI. Fig. 27,) cutting only reef 
flats which owe their existence to the extensive denudation of tho lower 
islands which once formed a line of hills reaching across that part of 
Torres Strait on the plateau formerly connecting Australia and New 
3uinea. 
An examination of the sections along the passes through tho Great 
Barrier Roef, (Plato XXXVII. Fig. 5, Plate XXXVIII. Figs. 10, 12, 
Plato XXXIX. Fig. 17, Plate XL. Figs. 20, 23, 24, 26,) show a very 
VOL. XXVIII. — NO. 4. 4 
