404 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Mar. 7, 



surfaces of which gold is visible), derived from decomposed granite, 

 together with fragments and pebbles of granite, quartz, altered schist, 

 grit, and an enormous amount of coarse garnets, spinelle rubies, 

 white topazes, blue and black tourmalines, some oxide of tin, native 

 white iron highly magnetic, cornelian, sapphires, chalcedony, &c. 



The river rises near the summit of the Dividing Range, in the 

 midst of a kind of plain or plateau, and winds amidst the rugged 

 blocks of hornblendic granite, until it descends to a somewhat lower 

 level where it forms flats with deep water-holes, in which the detritus 

 is accumulated. The ranges above this lower stage are nearly on a 

 level with the plateau at the head of the river, and these ranges are 

 crested by basalt, which has issued from and overflowed the granite. 

 The gold-washings are at the height of 2800 feet above the sea, by 

 my barometric observations, and the crowning basalt has an elevation 

 of 3085 feet. 



The contour of the country and its geological structure render it 

 probable that these bombs above mentioned had their origin in the 

 outburst of the trap. 



About four miles further south are the relics of quartziferous 

 schists and their associated grits, which have been transmuted by 

 the intrusion of various trappean, porphyritic, and trachytic rocks ; 

 and, though no direct crater is traceable, there is evidence of power- 

 ful igneous action*. As the detritus is all local, and there is no 

 easily-assignable crater, it seems most satisfactory to conclude that 

 these bombs are connected with the trap-eruption of the neighbour- 

 hood. This seems also in accordance with the facts mentioned by 

 Mr. Darwin respecting the structure and products of Ascension, where 

 such bombs are frequent, and basaltic streams cover other igneous 

 products, some of which are trachytic. 



Whether this explanation is sufficient or not, the facts themselves 

 are interesting ; for these singular bodies have been found in three 

 localities in Australia, at intervals of 455 and 205 miles apart, — 

 the distances from the Murray and Darling Plain to the Turon, and 

 from the Turon to the Uralla. That they could have had only one 

 point of origin is scarcely to be supposed, if they are really of sub- 

 aerial volcanic origin : in two of the three localities, at least, there 

 is presumption of such action ; and in both of these localities the 

 bombs were imbedded in gold deposits. 



* This district and the geological phaenomena are described in my Report to 

 the Government of New South Wales on the " auriferous character of the 

 country between the heads of the M'Leay and Gwydir Rivers," No. VII., dated 

 Armidale, 14th Feb. 1853. 



