THE AUSTRALIAN GREAT BARRIER REEF. 127 



which it probably originated. No mention was made, while tracing its course from 

 its beginning, a little north of Sandy Cape, of the few isolated islets and detached 

 reefs that occur at more or less remote distances from its outer border. The Portlock 

 reefs, lying some thirty miles to the north-east of the Flinders' Entrance, are the most 

 northern group. The Boot reef and the so-called Eastern Fields are intersected by 

 the parallel of 10° S., at distances of thirty and seventy miles from the Barrier outer 

 margin. 



With the exception of the somewhat ill-defined Ashmore reefs, ten miles south of the 

 Boot reef and a little nearer to the Warrior, the chart is a blank until the neighbourhood 

 of the Raine Island entrance. Within the area, embraced by thirty miles north and forty miles 

 south of this point, the edge of the Barrier itself is broken up in such manner as to form 

 a series of irregularly projecting prominences, and of reef-masses, that are completely separ- 

 ated by deep-water channels from the main bodj' of the Barrier. The Great Detached reef 

 that forms the outlying southern boundary to the Raine Island entrance is the most con- 

 spicuous. It is of an irregular elongate outline, about twelve miles long with an average of 

 five miles wide, but with a projecting central loop on its weather, or eastern, side. With the 

 exception of its lee, or northern side, it is bounded by a continuous mass of reef that 

 encloses a lagoon of from twenty to thirty fathoms deep. The lee, or inner, side, from which 

 entrance may be gained to the lagoon, is an irregular bank of soundings, with scattered 

 reef patches growing on it. Between this Great Detached reef and the main body of 

 the Barrier there is a channel five miles wide, throughout which a bottom of 105 and 135 

 fathoms were obtained at two isolated points during the Fly's survey. Six miles south of 

 the Great Detached reef, and between three and four distant from the Barrier margin, is a 

 second detached reef of irregularly circular outline, and about three miles in diameter, which 

 is known as Yule's Detached reef. This reef, as first described by Mr. jukes, "rises from 

 an unknown depth greater than one hundred fathoms, and seems to have a deep lagoon in 

 the centre into which there is no entrance." Special interest is attachable to these two 

 detached reefs. They illustrate the existence of true atoll reefs in intimate association 

 with the Great Barrier system in contradistinction to the atoll-like or false-atoll reefs 

 exemplified by the separate elements of the Capricorn and the Bunker Island groups, within 

 the southern area of the Barrier's border, referred to on a previous page. 



The margin of the Great Barrier, immediately adjacent to Yule's Detached reef, is one 

 of those irregular divergent projections from the almost rectilinear contour that most usually 

 distinguishes its outer rampart. This projection, which is about ten miles long, describes 

 a curve in a south-easterly direction ; and, a similar crescent-shaped projection being developed 

 towards its apex from a point a few miles farther south, in a north-easterly direction, they 

 enclose, between them, an almost circular area, about twelve miles in diameter, which is known 



