THE GREAT BARRIER REEF OF AUSTRALIA. 323 



coral skeletons or 'coralla' of a great number of closely associated 

 sea-anemone-like polyps. The closely aggregated clusters of our 

 commoner British species, such as the strawberry (Actinia 

 mesembryanthemimi), the daisy (Sagartia bellis), and the opelet 

 anemone (Anthea cereus), as they repose extended in their beauty 

 in some clear rock pool on, say, the Devonshire, Welsh, or Channel 

 Islands coast, have been a frequent source of admiring wonder. 

 The majority of the clusters have been formed by the repeated 

 subdivision, or technically termed * fission,' of a single primary 

 anemone or polyp. Supposing that these clustered anemones 

 secreted a calcareous coral basis, and, in place of becoming 

 entirely separated from one another, remained united by their 

 basal, skeleton-secreting tissues, we should have in this 

 hypothetical compound organism a precise presentment of the 

 structural organisation of a typical reef-forming coral." 



The highest elevation at which corals are found growing 

 within the Barrier-reef area is that of about ordinary low-water 

 mark. Thence downward to a depth of from twenty to thirty 

 fathoms represents the generally recognised bathymetrical range 

 of reef-coral growth. Their most luxuriant development, how- 

 ever, is limited by a depth of about fifteen fathoms from low- 

 water mark — an area that corresponds essentially with what is 

 known as the Oar-weed or Laminarian zone of European and 

 other temperate seas. 



The specific varieties of coral-reefs that receive universal 

 recognition at the hands of biologists are, as originally classified 

 by Mr. Darwin, referred to three distinct categories. These are — 

 (1) Lagoon islands, or Atolls ; (2) Barrier- or Encircling-reefs ; 

 and (3) Fringing- or Shore-reefs. Dealing with each of these in 

 turn, Mr. Saville Kent proceeds to discuss Mr. Darwin's theories 

 of reef formation, and to compare them with the views of more 

 recent writers on the subject who have been unable to accept 

 them. 



Then follows a consideration of the general structure and 

 most probable mode of origin of the Great Barrier Reef of 

 Australia, the most colossal of its kind. This is, naturally, one 

 of the longest chapters in the book, and a very interesting one ; 

 inasmuch as the evidence afforded by this great reef is for the 

 first time fairly and fully considered with a view to explain the 

 divergent views held by Mr. Darwin and Dr. John Murray in 



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