ANNIVERSARY ADDRESS OF THE PRESIDENT. xci 
with holes and hollows, in which living corals are growing. Coarse 
sand occurs inside the barrier and near the reefs, while finer matter 
is found more towards the main-land. 
We have here upon a great scale, occupying an area which may be 
roughly estimated at 30,000 square miles, that variable mixture of 
organic, mechanical, and chemical accumulations which has been so 
often remarked among coral reefs and islands, and of which Mr. Dar- 
win has given so valuable a summary, illustrated with such important 
original reasoning, in his work on Coral Islands. Although it would 
be out of place here to enter into the interesting details afforded by 
Mr. Beete Jukes, it is important to notice that he found corals able 
to sustain life when left by the tide several inches out of the sea. 
He observed living Astreeze, the tops of which were 18 inches above 
water, and he believes that an exposure to the sun and air for two 
or three hours will not kill many coral polyps, the cells retaining 
moisture so long as they are in a position of growth. 
When we consider the accumulations of the great barrier reef as a 
mass of matter obtained by animal life for its uses, havmg formed the 
hard parts needful to it, (including the shells of molluses, the spines 
and coatings of echinoderms and the like,) before it became sand, and 
furnished the materials for chalky and calcareous mud, or crystallized 
out in fitting situations and under the proper conditions, we are 
forcibly struck with the means by which the same matter has pro- 
bably passed from the solid form, (often perhaps from the fossil re- 
mains of pre-existing life,) into solution, whence it was abstracted by 
the coral polyps, molluscs and other creatures for their wants, again 
to be accumulated in a solid form, partly in that given to it by animal 
life, partly as sand and fine mud, and partly in a crystalline state. 
Mr. Darwin has pointed out the mixture of organic and mechanical 
matter forming -coral islands, the growth of the reef-making corals 
outwards, their abrasion in part by the breakers, and the accumula- 
tion of an outside talus at a high angle, over which the living corals 
gradually extend, and cover the fragments and worn portions by masses 
of their calcareous secretions. The observations of Mr. Beete Jukes 
would confirm these general views, but at the same time he remarks 
on the possibility of corals, with whose habits we may still remain un- 
acquainted, laying the foundation of reefs and islands in deeper water 
than is assigned to the existence of the known reef-constructing corals 
which flourish from near the surface of the sea to the depth of twenty 
or thirty fathoms. 
In the examination of Heron Island, the coral beds, one to two feet 
thick, were observed by Mr. Beete Jukes to have a tendency to split 
into slabs, and joimts were found to cross each other at right angles, 
parallel to the dip* and strike respectively, dividing up the coral rock 
into blocks of one or two feet in the side. This jointing of an accu- 
mulation, forming as it were under the eye, has no small geological 
bearing. 
It is interesting to consider the accumulations now collecting for 
1000 miles inside the outer ridge of the great barrier reef. The surf- 
* The dip was from 8° to 10°. 
