Geology.] 
NATURA[. HISTORY. 
Oil 
Morgan’s Island, in Blue-Mud Bay, north-west of Groote 
Eylandt, is composed principally of clinkstone^ sometimes 
indistinctly columnar. But among the specimens are also 
a coarse conglomerate of a dull purplish colour, — including 
pebbles of granular quartz and a fragment of a slaty rock 
like potstone : the hue and aspect of the compound being 
precisely those of the oldest sand-stones. Reddish quartzose 
sandstone^ of uniform and fine grain. A concretion of 
rounded quartz pebbles, cemented by ferruginous matter, 
apparently of recent formation. 
Round Hill, near Cape Grindall, — a prominence east of 
north from Blue-Mud Bay, was fourid by Captain Flinders to 
consist, at the upper part, of sandstone. The specimens of 
the rocks in its vicinity are, dark grey granite^ somewhat ap- 
approaching to gneiss, with a few specks of garnet ; and a 
calcareous, probably concretional stone, enclosing the re- 
mains of shells, with cavities lined with crystals of cal- 
careous spar. 
Mount Caledon, on the mainland, west of Caledon Bay, 
consists of grey granite^ with dark brown mica in small 
quantity ; and on the sides and top of the hill ‘ large loose 
blocks of that rock were observed, resting upon other blocks.’ 
A small island, near Cape Arnhem, is also composed of 
granite, in which the felspar has a bluish hue. 
Smaller of the Melville Islands, north-east of Melville 
Bay — A botryoidal mass of ferruginous oxide of man- 
ganese, approaching to hematite ; the fissures in some places 
occupied by carbonate of lime. 
* The relative position of the islands and bays on this part of 
the coast is represented in the enlarged Map, p. 600. 
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