160 GEOLOGY OF QUEENSLAND COAST, 



striking feature of these elevated flats, and islands connected by 

 sand ridges are common on the north-eastern side. 



Goold Island \^ 1,400 feet in height, and composed of granite 

 of acid type. Here, as at the Palms and Hinchinbrook, quartz 

 porphyry is a common rock-type, weathering generally into rect- 

 angular blocks, at times simulating the structures observable in 

 stratified rocks, thus differing from the ordinary spheroidal and 

 dome-shaped masses characteristic of granitic weathering. 



Dunk Island is of small extent, and covered with a dense 

 jungle or "brush." It consists of Silurian slates, quartzites, tuffs 

 and schists, and lies some five miles distant from the mainland, 

 which at this point also is composed of similar rocks, and supports 

 exceedingly dense forest and jungle growths (Fig. 6). 



Fig. 6. — Section across Dunk Island. 

 a. Present reef. />6, Coastal plain 20 feet above sea-level. c. Canon, 

 20 feet deep, exposing section of coastal plain. d. Contorted rocks (slates, 

 schists and quartz rocks). 



Horizontal Scale, 1 inch =250 yards. 



The island proper consists of high rough land meridionally 

 disposed. On the side facing the mainLand (leeward) a most 

 interesting flat occurs. It is between one and two miles in 

 length, and 500 or 600 yards in width. A low bench, two or 

 three feet above high water mark and several chains in width, 

 accompanies it for a considerable distance on its seaward edge, 

 and to this the flat presents a mural front 20 feet in height. Its 

 structure, as revealed by an examination of the seaward edge, 

 and that exposed in a 20 feet section made by a small canon 

 cutting across its breadth is that of a stiff clay, or clay and sand 

 admixtures, containing numerous angular and subangular frag- 



