SOUTH AUSTRALIAN GEOLOGY.  No. 2 - MOUNT SCHANCK.

It will be remembered that in explaining the geological features of Mount Gambier I stated -
1. That the lava arising from the eruption had in all probability flowed underground towards the sea.
2. That in doing so it deprived the overlaying limestone of support, causing it to fall in, and giving rise to the basin which is now known as the blue lake.
3. That the eruption from the chasm so made gave rise to the present walls.
It is necessary that these particulars should be borne in mind, because, as they were theories formed previous to an examination of the country between the mount and the sea, it is now necessary to judge how far they are supported by actual observation. Mount Schanck, as seen from Mount Gambier, appears like a truncated cone, rising abruptly from an apparently level plain. There are no mountains near lending to break the suddenness with which it appears on the field of view, and its darkened outlines readily suggest to an observer an extraordinary origin. The country around is well, almost thickly wooded, but the general aspect is fertile and pleasing, even seen from a distance. It is about eight miles, or even less, from Mount Gambier, the sea being about seven miles further on.

I have said almost enough in my last notice about the latter mount, but I cannot refrain, in taking leave of it, from mentioning the very beautiful view that is to be obtained from its summit. Below you the blue lake, with its smooth dark waters, and a little to the east the white houses of the township, peeping out from amid the trembling branches of the trees; all about green patches, which wave more and more in the breeze as the harvest approaches; whilst many a curling column of smoke, or the echoing of the whip in the forest around, tells that the new colonist is making a homestead where industry has never toiled before. To the north Leake's Bluff rises, while the outlines of Mount Mclntyre show more dimly on the sight, and then a third blue line, extending from the west to nearly south-east, shows where the ocean limits this part of South Australia. Mount Gambier is not very high, but the country is so uniformly level that a very small elevation gives an extensive field of view. Descending from it, and making for the cone with which we are at present occupied, one is astonished at the rich, the meadow-like appearance of the country. After being out some time in these colonies one becomes used to a certain dried-up appearance in every landscape, and learns to forget the flowery pastures, which used to meet the eye at home in June, and at the sight of the country here the old ideas come back with vividness. Here is meadow land as thickly studded with the buttercup and blue-bell as the finest hay-field at home. Beautiful is an adjective which comes short of the reality, and I doubt whether Somerset, or Kent, or Leicestershire could produce finer meadow land than the country between Mount Gambier and Mount Schanck.

There is rather an extraordinary appearance seen in the rocks about halfway between the two mounts. There are three well-shaped holes in the ground close to each other, and though they descend perpendicularly no bottom can be found. One is about a yard in diameter, the two others being less, and through the moss which covers the sides one can easily see that the fossiliferous limestone has been bored through. If you drop any solid substance down it can be heard rumbling for some distance, the noise growing gradually fainter till it dies away, but no stoppage of any kind can be detected. Knowing that the lava has passed underground in this direction it would not at first sight seem unreasonable to attribute their origin to steam arising from the melted liquid. But this would, perhaps, be too easy a theory to be correct. There is as great difficulty in accounting for them as the celebrated sandpipes in the chalk; but as they occur in other places where there is little probability of the existence of lava, they could scarcely have arisen from steam. Posibly filtration may have been an agent, but this is mere conjecture.

As our volcano is approached the ground becomes broken and very hilly. The soil, too, is less rich, as evidenced by the quantity of stringybark (eucalyptus fabrorum) and grasstree (Xanthorrhea Australis). The ferns and underwood also become thick and intricate. By-and-bye large blocks of porous lava are seen strewn on the ground, the peculiar brown ash-dust rising under the horse's feet as you cross the numerous abrupt spurs which run out from the base of the cone. On ascending the steepest of these a dense tangled mass of vegetation comes into view, evidently surounding some hollow below. Descending towards it (not without care, for the ground, hidden by the ferns, is treacherous and steep, and one is nearly swept out of the saddle by the brush, which almost meets above the horse's head), and taking a sweep round to make the descent more easy, the bottom is reached, and a beautiful little lake comes in view. Situated as it is in a kind of dell, it wears a most silent, solitary aspect; but as the lava boulders and limestone rocks jut out from the dense and high brushwood in black and white patches, as the occasional slopes of silver grass gracefully interrupt the thicket, the appearance is more beautiful than sublime. It is one of those places where the beauty of the Australian flora can be seen to best advantage. The tall dark tea-tree (melaleuca paludosa) reflected in the smooth water; the ferns and mosses, which make a carpet underneath the mimosa; the Burgaria spinosa and calycathrix scabra, with its bushy pink flowers, filling up the interstices in the brush; the whole united by the delicate tendrils of the comespermia volubilis, with its network of blue blossoms, make a scene as beautiful in its kind as the vineyards of Provence or the rich palm scenes of the Torrid Zone. No better idea could be formed of this little place than from Sir W. Scott's description of that dell whence issued the skiff of the Lady of the Lake, and had South Australia been long enough inhabited, the spot would have been invested with traditionary legends, perhaps making it a resort of frolicsome faries.

This little lake has arisen from a small eruption that has proceeded from its centre, probably at the time Mount Schanck was in activity. Very little lava or ash has come from it. Of course some has come, and the sides being very near the point of eruption, the ejectamenta deposited immediately after their egress in a partially fused state have formed layers of lava, which evidently commenced flowing back to the crater before cooling. This This all that is found. In some places the trap lies in layers just as it cooled, and in others it is broken up into boulders. It is very porous, but more so on the top of the layer than underneath. The latter fact is easily explained. The pores arise from the escape of gases from the melted fluid, and these gaseous bubbles would naturally rise to the surface, but as the portion exposed to the air would cool first, a cake would be formed on the surface which would prevent the exit of the bubbles, and so they would remain after cooling in the shape of almond-like holes in the stone. At the north end of the lake and on the east side the limestone is not covered with ash, but stands on in small escarpments even far above the level of the lava. It is blackened, and was not formerly fossiliferous, being of the uppermost limestone strata, which in the formation seldom contains many shells. Probably the reason why it stands so far above the water level and in broken masses is because the spot was disturbed by a small explosive earthquake before the eruption broke out, and its perpendicularity explains why it was not covered with ash or lava. It is evident that this lake was not so much an eruptive crater as a spot whence issued steam and a small quantity of ashes. Such a phenomenon is not unusual in volcanoes. There is one by the side of Vesuvius which, though it sends forth ashes occasionally, confines its operations nearly entirely to steam. There is another by the side of Etna. What is the cause of them, or why the main crater is not a sufficient outlet for the steam, is not well understood, though when they occur independently of volcanoes (such as in the case of the Suffioni, in Tuscany) an explanation has been readily found. The one now described is certainly one of the supplementary points of egress, for had it been a proper crater it is quite large enough to have given rise to a very large quantity of ash, whereas at present the walls do not rise above the plains.

At the side of the lake the cone of Mount Schanck rises abruptly. The ascent is very steep, and, though covered with thick grass, is only dotted with trees. Occasionally a broken fragment of porous lava is met with, but with these exceptions smoothly sloping. Going to the top of the cone (no easy matter, for the inclination is steep, and the height, about 300 feet), you stand on the edge of the crater. It is a deep dark abyss, the walls round forming; a complete circle of almost equal height. Its aspect ia entirely different from Mount Gambler, though quite as grand. There is no water at the bottom to give it that placid look of loneliness which the other volcano possesses; but the dark stone walls, occasionally covered by a verdure which the shade makes darker still, the suddenness of the descent, and the yawning look of the chasm, give it a wild sublimity, grand and awful of its kind. The whole depth of the crater does not probably bring it much, if at all, below the level of the limestone strata. The sides are seen from the interior to be formed of regular layers of ash, which has hardened into an ash conglomerate, as at the higher wall of Mount Gambier. In some cases there has been a backward flow of the lava which has bubbled out, in which case it appears twisted into strange wreaths, looking like the gnarled roots of some huge tree. The sides are nearly entirely covered with vegetation except near the top, but there are places where the black ash is undecomposed, and does not bear a sign of vegetation from the top to the bottom. Looking down the crater is exactly like looking into a large funnel, so very narrow is the bottom in proportion to the rim. There is no break in the side, nor outlet of any kind for lava; in fact, the whole process of the eruption seems to have been limited to throwing up masses of ash until it had burned itself out. It is interesting, however, to know that the state in which the crater is now seen is probably the appearance it wore (with the exception of the vegetation) at the time of its activity. Thus, when Sir H. Davy visited Vesuvius, he says that whenever the smoke cleared away, and he could look down to the bottom of the crater, there was no fire to be seen, but it appeared like a deep black funnel coming to a sharp point, from which smoke and steam were rising. Every now and then a noise like distant thunder was heard, which, coming nearer, seemed to end in an explosion at the bottom of the crater, casting up volumes of ash into the air, and then all was quiet again. The crater of Mount Etna, as described by Sir William Hamilton, seems to be just similar - a dark funnel, with no fire visible, casting up ash in occasional explosion. Thus, it appears that both resembled in their quiet state the present aspect of Mount Schanck.

I have said there is no outlet for lava visible. It remains to be asked, was there any flow? or, did this volcano owe its origin to a passage of lava from Mount Gambier to thesea? With regard to the latter, I think not. It is true that lava did, as I supposed, flow underground; but it has come to the surface close to the present crater, clearly showing the latter mount to have an origin of its own. About 100 yards from the base of the cone there is a space of broken ground, about 40 yards in width, and about three quarters of a mile long. The width seems to be about equal during the whole length. When I say broken ground, I mean ground, not only broken up into hillocks, but also covered throughout its length and breadth with fragments of scoria; from one to three feet in diameter. Sometimes these small boulders are gathered into mounds, as though piled up by art, and again they are found lining a deep hollow; but whether rising into hillocks, or scattered about as if thrown from one centre, they all keep a regular line, at times diverging from due north and south, but only to make a slight curve, and then return to the original course. It appears, in fact, like the course of a liquid, and this was really the case. It will be remembered, that when I supposed the lava from Mount Gambier to have flowed underground, I mentioned the instance of the volcano of Kilauea, where the lava, after flowing underground, came to the surface about six miles from the point of eruption, and ran along the ground for some distance. Such has been the course here. It will be seen at once, on examining the ground, that the scoria could not have arisen from the adjacent crater, because it takes its origin much to the north of it, and then runs along in an undeviating line till at least half a mile past it. It need hardly be stated further, that if it came from the crater, it would be scattered at least halfway round in a semicircular form, the larger fragments being nearer the cone. But it is not so. There is a regular straight line, nearly north and south, occupying only one side of the volcano, and pursuing its course quite independently of it. This line of lava was then a current from Mount Gambier, but it is not easy, in supposing it to be so, to account for the broken undulatory character of the scoriae. I have said the pieces were piled up together, and sometimes seemed to surround hollows in the ground. Two ways in which this state of things could have been produced suggest themselves to me. The first and more probable one is that the first flow of lava has been heaved up after cooling by a second current running underneath. This would raise the stone almost upright in slabs, and probably, if they broke afterwards, they would form the piles of scoriae which are seen. A second cause might be the explosion of disengaged gases, when the upper part of the current had cooled and the under still flowing. This latter cause the chemical properties of the lava would render likely. Phosphoretted hydrogen and sulphuretted hydrogen, both being very explosive, can be naturally supposed to have existed here. The former, by the action of heat and sulphuric acid on the phosphate of lime contained in the highly fossiliferous rocks; the latter, by the decomposition of the water contained in the moist earth on which the lava flowed; the fluid itself, in both cases, supplying the sulphur.

In what way, it will be asked, is Mount Gambier connected with Mount Schank. No other relation is visible than their contiguity. There is, however, one remote connection, and that is, that these volcanoes belong to a group which extends nearly west from Geelong. There is a complete chain of extinct craters from the latter place to the South Australian boundary, concluding westward with Lake Edward and Lake Leake. These latter are two waters lying about N.N.W. of Mount Gambier, which is about due N. of Mount Schanck. Lake Leake is a large crater, but one which has given rise to so small a quantity of ash that its volcanic origin would not be suspected, unless it were closely examined. The only ejectamenta form one little eminence of tufa, scarcely rising 50 feet above the plain. Lake Edward is similar. Both are filled with water, and are pretty deep, but neither seemed to have much disturbed the country near. The general course of the disturbance seems to be nearly east and west, and the most westerly point where volcanic evidences are seen is at Mount Graham and Mount Muirhead. These are both upheavals caused by dykes of trap, and the tops of the mounts consist of that rock. Here the difference is seen between trap which flows on the ground, such as at Mount Schanck, and that which is forced up at a great pressure. In the former case, large blocks can be easily lifted in one hand; in the latter, small pieces are extremely heavy. Mount Muirhead is erroneously described as a crater in Mr. Bonwick's map. The whole disturbance on either side of the boundary between the two colonies seems to belong to one period; for the trap is always found overlaying the secondary limestone. Once the Glenelg is crossed, the country is one mass of basaltic trap, which continues as far south as Portland, where it is found even on the very edge of the cliffs, whose base is washed by the sea. I have said before that it is comparatively modern, perhaps since the creation of man, for the blacks seem to have some tradition of the former fiery activity of Mount Gambier; but I may safely say that either this or any trap about here can give not the slightest clue to the discovery of gold. The trap found on the diggings belongs to the same period apparently; but, in any case, is in no way connected with the gold underneath; for the cause which gave rise to the former was subsequent to the latter. I mention this for the information of those who think that Mount Gambier might hereafter prove an auriferous country. Though trap is sometimes found near gold it never has any more connection with it than two phenomena totally distinct happening in the same place.

I mentioned formerly that the lava arising from Mount Gambier was found, under the cliffs on the coast. I am now sure that it is too far east to have come from that mount. Some is on the coast from the latter I am sure; but the sand has silted up so much as to obliterate any former trace that may have existed.

My descriptions of this volcanic country are finished, for Mount Schanck is the last which lies between the interior and the sea. Whatever other traces exist on the coast is difficult to say; for the sand, as I have just remarked, is drifting up so fast that even trees are buried in its encroachments. The coast-line, is seen from the coast, is barren and dismal enough; but on a closer view, it bears so wild and lonely an aspect as almost to make one shudder. Large and dreary swamps, covered over with dank vegetation; white sandhills, bearing patches of salt-bush; cold and gloomy cliffs are all that meet the eye; and the sea breaks in with such a heavy surf that even in calm weather its solemn roar may be heard for miles around. Seldom human being visit it, and when a vessel was wrecked there some time ago the poor wretches who escaped drowning fell to pieces from the ropes to which they clung before their remains were discovered. Forlorn and sad as it is, nothing could be more in keeping with such solitude to think that there volcanic fires rolled in times gone by. A long time ago it must have been; how long, indeed, may perhaps, perplex mankind till time shall be no longer. A thin seam of shells in the sands far above the water tell us that even the sea has retreated since then; that the waters now surging at a distance were once beating their monotonous music on the spot where we stand, bringing into competition the noise of fires and the rush of waters. The stones, so full of strange histories, tell us that it is a long time since the fires rose; and the trees and flowers, quietly growing on the softened rock in the crater itself, tell us by their tranquil growth that the fire has long since fulfilled its Author's work, and disappeared, leaving for ages the black and empty chasm staring into the heavens, lonely and desolate.