CHAPTER XIII. 



EXTENT OF THE BARRIER REEFS— THE INNER AND OUTER 

 ROUTES — GENERAL FEATURES OF AN " INDIVIDUAL CORAL 



REEF" MODES IN WHICH THESE REEFS ARE GROUPED 



THE REEFS OF THE GREAT BARRIER DIVIDED INTO THREE 

 KINDS: — FIRST, LINEAR OR BARRIER REEFS; SECOND, 

 DETACHED REEFS; THIRD, INNER REEFS — FORM AND 

 EXTENT OF THE GREAT BARRIER REEFS — LIKENESS TO A 



SUBMARINE FORTIFICATION NORMAL FORM OF THE 



GREAT REEF-MASS — VARIATIONS FROM THAT FORM — THE 

 CORAL CONGLOMERATE AND PUMICE PEBBLES OF THE 

 NORTH-EAST COAST OF AUSTRALIA— STRUCTURE OF RAINE's 

 ISLET — SINGULAR MASS OF POINTS ABOVE HIGH-WATER 

 MARK ALL PROVE STATIONARY CONDITION OF NORTH- 

 EAST COAST FOR LONG PERIOD OF TIME MR. DARWIN's 



THEORY APPLIED TO THE GREAT BARRIER — EXPLANATION 

 THROUGH IT OF BOTH THE GENERAL FORM, THE NORMAL 

 CONDITION, AND THE OCCASIONAL EXCEPTIONS AND 

 VARIATIONS. 



I shall, in this chapter, give a general sketch of 

 the structure of the Great Barrier reef, as far as it 

 was known at the close of our survey in the year 

 1845. It may be said to commence with Breaksea 

 Spit, in S.lat. 24° 30', E. long. 153° 20', and extend 

 to Bristow Island, on the coast of New Guinea, in 

 S. lat. 9° 15', and E. long. 143° 20'. This would 

 give, in a straight line, a distance of about 1100 

 geographical miles, or about 1260 statute miles. It 



