Xe PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 
amount of vegetable matter to form it, and another coal bed was 
found in Cumberland Bay. Fossil wood is also noticed as scattered 
through the igneous rocks. How far some of these rocks may be 
consolidated ashes does not appear, but it might well happen, that 
not only lava-currents may have flowed over a mass of vegetation, 
perhaps sometimes a thick peat-bog, but also that a body of ashes 
may have been vomited over them from a neighbourmg crater. 
Whether enveloped by ashes, subsequently consolidated, or by molten 
rock, the conditions for silicification of some of the wood remind us 
of those in Tasmania. The prevalence of the remains of a vegetation 
now no longer found is a fact of much geological interest, for we can 
scarcely doubt, from their mode of occurrence, that the plants en- 
tombed grew on the spot. Here, therefore, upon a small pomt of 
land, projecting through the waters of the southern ocean, far remote 
from continents (that of Victoria Land being probably the nearest), 
we have evidence of changed conditions regarding the growth of 
plants. The mere chance of such an investigation as could be given 
affords the remains of a tree seven feet in circumference, in a region 
where small plants only can at present grow, and we are left to infer 
that when such trees flourished a milder climate reigned over this 
land, now so desolate. 
Mr. Beete Jukes has, in his account of the voyage of the ‘ Fly’ to 
Torres’ Straits and Australia, furnished us with much valuable in- 
formation respecting that coral accumulation known as the Great 
Barrier Reef, which extends for about 1000 miles in length, with 
about 30 i mean breadth, from Breaksea Spit, off the eastern 
coast of Australia, in lat. 24° 30! S., to Bristow Island, off the coast 
of New Guinea, in lat. 9° 15'S. During the needful examinations 
by Captam Blackwood, in command of the surveying expedition, 
Mr. Beete Jukes lost no opportunity of studymg this imteresting 
mass of matter, due to the power of myriads of polyps to obtain from 
the sea and secrete carbonate of lime. He divides the accumulation 
into, lst, linear reefs, forming the outer edge or actual barrier; 2nd, 
detached reefs, outside the main barrier ; and 3rd, inner reefs between 
the shore and the barrier. The lmear reefs vary from half a mile to 
15 miles in length; the detached reefs take more or less the circular 
or oval form, with lagoons inside, to which Mr. Darwin has assigned 
the name of afol/s, and the outlines of the inner reefs are noticed as 
of different shapes. On the outer side of this great mass of coral 
accumulations, or of matter derived from them, the sea suddenly be- 
comes deep, while on the inside it is comparatively shallow. The 
edges gradually slope, or are rounded to the depth of 12 or 24 feet, 
after which they plunge with equal slopes suddenly into 120 to 1200 
feet, as the case may be. On the weather, or more exposed side of 
the reef, great blocks of coral, six to nine feet across, are detached by 
the force of the breakers from the main mass, and the surface of the 
reef is described as having the appearance of a great flat of sandstone. 
Loose slabs lie abgut, with here and there an accumulation of dead 
coral branches, or banks of white sand, and the whole is checkered 
« 
