XCl1V PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 
of a part of the Eastern Australian and Torres’ Straits’ coral accumu- 
lations. Volcanic substances are mingled with white limestone, some 
of the pieces of the latter and of lava even showing that they have 
been rounded. In Erroob, rocks that have been in a molten state 
are seen to cover the sandstones and conglomerates. These volcanic 
vents at the northern part of the great barrier reef are supposed to 
form part of a great belt of volcanic operations, ranging at no great 
distance to the northward and eastward along the north coast of New 
Guinea into the Solomon Islands, New Hebrides and New Zealand. 
As connected with the formation of the present reefs off Eastern 
Australia by slow depression of the land, thus causing the corals to 
raise the reefs in proportion as the general mass of land and the neigh- 
bouring shore sank down, in the manner by which Mr. Darwin 
accounts for the atolls and barrier reefs round many islands, our 
author points out a fact of much importance. There are flats of 
coral conglomerate, half a mile wide, frequent on the north-eastern 
coast of Australia, in and upon which, and upon other flats of the 
same coast, pumice pebbles are abundantly scattered, about ten feet 
above the present high-water mark. Indeed these pumice pebbles 
are found at the same elevation for nearly 2000 miles along the east- 
ern coast. Hence Mr. Beete Jukes infers the coast to have been 
equally affected as regards elevation or depression since these pebbles 
were accumulated, and that it has been slightly elevated, or at least 
has not suffered any depression during a long period of time. He 
allows for the pilmg action of breakers, which no doubt during the 
heaviest gales of wind throw pebbles on shore far beyond the usual 
average of high water, and would readily force before them such 
light bodies as pumice pebbles ; and during such times, no doubt, they 
could be easily floated over extensive flats covered by the sea. It 
would appear that these pumice pebbles are mingled with the coral 
conglomerates, and were noticed in the coral rock of Rame’s Island. 
The accumulation of pumice at one time more than at another 
would depend upon the nature of the supply, and would last no 
longer than the eruptions continued which produced it in some situ- 
ation whence it could be drifted to the Australian coast and be ground 
into pebbles. That there has been elevation and depression of the 
land and adjacent sea-bottoms in many localities in different parts of 
the world, producing the effects connected with coral reefs which 
have been pointed out by Mr. Darwin, is exceedingly probable: in- 
deed, respecting the elevation of coral reefs we have abundant proofs, 
and therefore there is little reason to doubt depression, which the 
accumulation of rocks of all geological ages shows to have been very 
common and often very extensive. Upon such points the geologist 
can have little doubt, but he may sometimes doubt the application of 
depression to every case of a barrier reef, seemg the power of exten- 
sion through long-continued time of the reefs outwards into deep 
water. The study of reef-making corals shows us how they seek 
clean water and the surf, and the manner in which they avoid waters 
charged with mineral matter in mechanical suspension. Hence we 
commonly find them either attached to, or at a distance from the 
