These signs of improvement, however, vanish the moment Mittagong range is crossed, and sand-stone again forms the basis of the country to a considerable distance beyond Bong-bong. At a small farm called the Ploughed Ground, it is again traversed by a dike of whinstone, and a rich but isolated spot is thus passed over. With occasional and partial interruption, however, the sand-stone formation continues to an abrupt pass, from which the traveller descends to the county of Argyle. This pass is extremely abrupt, and is covered with glaucus, the low scrub I have noticed as common to the sand-stone formation. A small but lively stream, called Paddy's River, runs at the bottom of this pass, and immediately to the S.W. of it, an open forest country of granite base extends for many miles, on which the eucalyptus manifera is prevalent, and which affords the best grazing tracts in Argyle. At Goulburn Plains, however, a vein of limestone occurs, which is evidently connected with that forming the ShoalHaven Gully, which is perhaps the most remarkable geological feature in the colony of New South Wales. It is a deep chasm of about a quarter of a mile in breadth, and 1200 feet in depth. The country on either side is perfectly level, so much so that the traveller approaches almost to its very brink before he is aware of his being near so singular an abyss. A small rivulet flows through the Gully, and discharges itself into the sea at ShoalHaven; but this river is hardly perceptible, from the summit of the cliffs forming the sides of the Gully, which are of the boldest and most precipitous character. The ground on the summit is full of caves of great depth, but there has been a difficulty in examining them, in consequence of the violent wind that rushes up them, and extinguishes every torch. The open and grassy forests of Argyle are terminated by another of those abrupt sand-stone passes I have just described, and the traveller again falls considerably from his former level, previously to his entering on Yass Plains, to which this pass is the only inlet. From Yass Plains the view to the S. and S.W. is over a lofty and broken country: mountains with rounded summits, others with towering peaks, and others again of lengthened form but sharp spine, characterise the various rocks of which they are composed. The ranges decline rapidly from east to west, and while on the one hand the country has all the appearance of increasing height, on the other it sinks to a dead level; nor on the distant horizon to the N. W. is there a hill or an inequality to be seen. From Yass Plains to the very commencement of the level interior, every range I crossed presented a new rock-formation; serpentine quartz in huge white masses, granite, chlorite, micaceous schist, sandstone, chalcedony, quartz, and red jasper, and conglomerate rocks.