140 bulletin: museum of comparative zoology. 



islands plainly indicates their former connection with the Australian 

 continent. 



It may not be out of place to examine now what light the hydrog- 

 raphy of Queensland throws upon the subject of the extension of the 

 rocks of the mainland to the outer edge of the Great Barrier Reef. To 

 elucidate this point I have prepared a series of sections taken from the 

 Admiralty Charts, extending from Moreton Bay to New Guinea (Plates 

 XXIII., XXIV., XXXVII. to XLL). 



The continental plateau off the east coast of Australia is a compara- 

 tively narrow shelf, varying in width north of Sydney between fifteen 

 and thirty miles, which is the distance at which we find the 100 

 fathom line, and where the slope becomes most abrupt, depths of 1,500 

 to over 2,000 fathoms are reached within short distances. The con- 

 tinental plateau widens somewhat to the east of the Capricorn Channel 

 (Plate XXXVII. Fig. 6), where it attains a width (its greatest width) 

 of nearly 150 miles. The outer edge then runs in a westerly direction, 

 gradually coming nearer the mainland (Plate XXXVI II.), to Flinders 

 Pass, where it is less than forty miles distant from the mainland. 



The outer edge of the Barrier Beef there takes a more northerly direc- 

 tion, gradually approaching still more the continental shore, and in 

 some places not being more than twelve to fifteen miles from it (Flate 

 XXXIX., Plate XL. Figs. 18-22) ; until somewhat south of Cape 

 Grenville, the outer edge of the Great Barrier Reef runs due north and 

 expands into the wide continental platform, from 100 to 110 miles, 

 which unites the Australian continent with New Guinea (Plate XL. 

 Figs. 23-26, Plate XLL). 



An inspection of the charts and of the sections cannot fail to show 

 that the pitch of the narrow continental shelf off the east shore of 

 Australia south of Sandy Cape (Breaksea Spit) is much steeper than 

 the sea slope of the continental shelf north of it. With the ex- 

 ception of a short distance parallel to the outer edge of the Great 

 Barrier Reef and extending from Lark Pass to off Capo Melville, the 

 1,000 fathom line is close to the 100 fathom line south of Breaksea 

 Spit to well beyond Sydney ; while north of Sandy Cape, with the 

 exception named above, the 1,000 fathom line forms a great loop to 

 the eastward, and is often 250 miles distant from the 100 fathom 

 line. So that, in the very region where the Great Barrier Reef 

 extends, the continental slope does not compare in steepness to the 

 pitch which characterizes it in the non-coraUiferous belt to the south 

 of Prazer Island. (Compare the different figures of Plate XXXVII.) 



