To find this small bed of the remains of shell animals, of which chalk is formed wherever found, in such an unexpected situation, excited some surprise; and Mr. Bass endeavoured to investigate the cause of this deposit, by examining the form of the neighbouring parts of the island.
The result of his inquiries and conjectures amounted to this: that as traces of the sea, and of the effects of running waters, were plainly discernible in many parts of the island, and more particularly in the vicinity of this deposit of chalk and granite, it seemed highly probable that it had been formed by two streams of the tide, which, when the island was yet beneath the surface of the sea, having swept round a large lump of rocks, then met and formed an eddy, where every substance would fall to the bottom. The lump of rocks is now a rocky knoll, which runs tapering from the opposite side of the island toward the chalk. On each side of it is a gap, through which the two streams appear to have passed.
The vegetation on the island seems brown and starved. It consists of a few stunted trees; several patches of brush, close set and almost impenetrable; large tufts of sour and wiry grass, and abundance of low saltish plants, chiefly of the creeping kind.
A small spot upon the east end of the island presented a phenomenon which seemed not easily explicable by any known laws of that class of natural history to which it alone was referable.
Amidst a patch of naked sand, upon one of the highest parts of the island, at not less than 100 feet above the level of the sea, within the limits of a few hundred yards square, were lying scattered about a number of short broken branches of old dead trees, of from one to three inches in diameter, and seemingly of a kind similar to the large brush wood. Amid these broken branches were seen sticking up several white stony stumps, of sizes ranging between the above diameters, and in height from a foot to a foot and a half. Their peculiar form, together with a number of prongs of their own quality, projecting in different directions from around their base, and entering the ground in the manner of roots, presented themselves to the mind of an observer, with a striking resemblance to the stumps and roots of small trees. These were extremely brittle, the slightest blow with a stick, or with each other, being sufficient to break them short off; and when taken into the hand, many of them broke to pieces with their own weight.
On being broken transversely, it was immediately seen that the internal part was divided into interior or central, exterior or cortical. The exterior part, which in different specimens occupied various proportions of the whole, resembled a fine white and soft grit-stone; but acids being applied, showed it to be combined with a considerable portion of calcareous matter. The interior or central part was always circular, but seldom found of the same diameter, or of the same composition, on any two stumps. In some the calcareous and sandy matter had taken such entire possession, that every fragment of the wood was completely obliterated; but yet a faint central ring remained. In others was a centre of chalk, beautifully white, that crumbled between the fingers to the finest powder; some consisted of chalk and brown earth, in various quantities, and some others had detained a few frail portions of their woody fibres, the spaces between which were filled up with chalky earth.
It appeared, that when the people of the Sydney Cove first came upon the island, the pieces of dead branches that at this time were lying round the stumps, then formed, with them, the stem and branches of dead trees complete. But by the time Mr. Bass visited the place, the hands of curiosity, and the frolics of an unruly horse that was saved from the wreck, had reduced them to the state already described.
Mr. Bass had been told from good authority, that when the trees were in a complete state, the diameter of the dead wood of the stem that rose immediately from the stoney part was equal to the diameter of that part; and also that a living leaf was seen upon the uppermost branches of one of them. But he could never learn whether the stony part of the stem was of an equal height in all the trees.
To ascertain to what depth the petrification had extended, Mr. Bass scratched away the sand from the foot of many of the stumps, and in no instance found it to have proceeded more than three or four inches beneath the surface of the sand, as it then lay; for at that depth the brown and crumbling remains of the root came into view. There were, indeed, parts of the roots which had undergone an alteration similar to that which had taken place in the stems: but these tended to establish the limits of the petrifying power; for they had felt it only either at their first outset from the bottom of the stems, or when, being obstructed in their progress, they had of necessity arched upwards toward the surface.
In attempting to account for the cause that had operated to produce this change in the structure of the lower parts of the stems of these trees, Mr. Bass feels the utmost diffidence. He found that all his conjectures which were best supported by existing facts, led him to place them among petrifications; although no strict analogy could be seen between them and the subjects usually met with of this kind.