Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/397

1869.] RATTRAY-CAPE-YORK PENINSULA. 301 creeks of the neighbourhood, where the soil is more alluvial and the vegetation more tropical. But even there it contrasts strongly with its vigour and abundance further south, where the soil is formed of the detritus of primary, metamorphic and sandstone rocks and shales, the water-supply more copious, and both the physical geography, geology, and climate more favourable for growth. The diminutive ants which abound here appear to prefer this ferruginous soil, which they convert into a hard sun-dried clay, to construct their peculiar pinnacled ant-hills, often 12 to 15 feet high, which form a conspicuous feature on the hillsides and landscapes of the vicinity of Somerset. It would be interesting to know whether or not this formation also extends, like the two former, across Torres Strait into New Guinea. Certainly a considerable patch of the southern part of that island immediately opposite Cape York, is a blank in our most trustworthy geological maps, which may yet be filled up by the formations now named. The overland expedition of the Jardines has proved that this rock is found as far south, on the west side of the mountain-range, as the Mitchell River; and it probably extends westward to the Gulf of Carpentaria, while on the east side of the range it certainly exists as far as Weymouth Bay. According to the Rev. W. B. Clarke, of Sydney, this rock "is post-tertiary, as it contains no gold; otherwise it most highly resembles the common ironstone in the auriferous rocks of New South Wales." A careful assay of an average specimen made for me by his instigation at the Royal Mint of Sydney, in March 1865, showed that the ore contained 39-69 per cent, of iron, but neither gold nor silver. Though capable of yielding a fair per-centage of metal, the absence of coal in the vicinity, the high price of labour, great distance, and cost of carriage of the former to and of the smelted iron from the settlement, will, however, long and perhaps always render this ore practically unavailable.

Lying between the volcanic rock beneath and the superimposed Posttertiary ironstone, we find a more local and limited deposit in the form of a coarse quartzose sandstone, having a wavy stratification, and composed of attrited fragments of quartz varying from ordinary sand particles to the size of a hazel-nut, imbedded in a light clayey matrix, very friable and unfit for building when weathered. Of this, several of the bold cliffs of Albany island and the opposite mainland consist; and these are so directly opposed, while the bluffs and bays on either side would dovetail so accurately if brought together, that we may fairly conjecture that they were once continuous, before the production of the huge cleft which now forms the Albany pass, or the upheaval of the crystalline rock beneath, which was doubtless the cause of this. A similar quartzose sandstone was also found by the Jardines at various places along their route, and there as here in connexion with ironstone. It would be interesting to know whether a like formation exists in the adjacent part of New Guinea. No fossils have yet been detected in this rock. At the north end of Albany island, where a boss of porphyry protrudes and displaces the overlying sandstone and ironstone, fine examples

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