xeil PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 
loving corals probably extend over broken or triturated coral outwards, 
slowly advancing the main mass. While great depths bound the outer 
edge the inside becomes filled up by a multitude of corals, which can 
there adjust themselves to the needful conditions ; and by coral sand- 
banks, which Mr. Beete Jukes shows are but “the washings of broken 
coral swept by tides and winds towards the lee side of the reef, until 
that is made the shallowest.”’ ‘‘ When this is dry at low-water, the 
sand is piled up by the wind into a heap, with a sloping bank, till it 
is at last reared above high-water mark.” 
Amid these corals and sand-banks, numbers of molluscs, radiata, 
and fishes live, and at death leave a large proportion of their harder 
parts, adding to the general accumulation, and often doubtless in a 
stratiform manner. Nor are these the only classes of animal life, the 
remains of which aid in increasing the general mass. Turtles frequent 
the reefs, banks and islets, where their skeletons and bones are found 
scattered, and the conditions are such that these remains can scarcely 
but be entombed amid the calcareous sands and coral growth. Their 
eggs are known to be so imbedded. The bones of birds also may 
probably be enveloped, for immense flights of them are seen on the 
islets. Raine’s Islet, mentioned as not more than 1000 yards long 
and 500 yards wide, and only 20 feet above the sea, was found 
covered with them. 
The conditions for the solution and chemical deposit of carbonate of 
lime would often arise, and a slight to and fro motion from a ripple 
in sheltered situations, where carbonate of lime was being thrown 
down from solution, would so roll about fine grains that they became 
covered by concentric concretions, forming oolites. Mr. Beete Jukes 
found such upon Raine’s Islet. Where circumstances were favourable 
the crystalline arrangement would be upon a larger scale, and definite 
forms would be presented. Our author found drusy cavities in coral 
rock containing crystals of carbonate of lime, as also some of sulphate 
of lime. 
While this order of accumulation was progressmg from the clean 
sea and outward reefs inwards, different conditions would obtain along 
the shore of the main land. It is well known to those who have 
studied coral reefs that most coral polyps cannot support life where 
the waters are charged with muddy matter or fine detritus. We have 
often had occasion to observe this fact around Jamaica. As the 
Australian coast is approached, notwithstanding that it is protected 
from the ocean breakers by the outer reefs, there is still enough 
abrasion by the sea to produce detritus, adding to that which may be 
brought down by the rivers. These are known to be of so little im- 
portance that water is scarce along the whole coast bounded by the 
coral barrier. Indeed if it were otherwise the barrier would be broken 
through, or rather would never have been formed where the muddy 
waters of large rivers interfered with the coral growth. 
Towards the coast, therefore, there would be conditions, antagonist 
to the growth of the reef-making corals, which would gradually cease 
towards the clear water outside the reefs. Though interfering with 
coral life, they would necessarily have no influence on the extension 
