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 steepest 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 XXXVII. 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 



XXXVII. Figs. 4, 7 ; Plate XXXIX. Figs. 13, 15 j 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 



XXXVIII. Figs. 8-10, Plate XXXIX. Fig. 16, and Plate XL. Figs. 

 21, 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 the 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 case the sections have been made across a district in which the 

 islands, while they have undoubtedly been greatly worn, yet 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 XLI.) across 

 the line of islands and reefs extending from the mainland to Xew 

 Guinea, and the section more 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 the lower 

 islands which once formed a line of hills reaching across that part of 

 Torres Strait on the plateau formerly connecting Australia and Xew 

 Guinea. 



An examination of the sections along the passes through the Great 

 Barrier Reef, (Plate XXXVI I. Fig. 5, Plate XXXVIII. Figs. 10, 12, 

 Plate XXXIX. Fig. 17, Plate XL. Figs. 20, 23, 24, 26,) show a very 



VOL. XXVIII. — NO. 4. 4 



