BY W. N. BENSON. 719 



other side of the area of older rock to the east. These are almost 

 identical, microscopically [see M.B., 76, and 263], and their clas- 

 tic nature is quite obvious. They are chiefly acid plagioclase in 

 crystals and grains, with a little quartz, and a finely felsitic ground- 

 mass. Considering the geological occurrence of the rock, there is a 

 surprising amount of crushing and bending of the felspar. Mag- 

 netite, chlorite, epidote, and calcite occur in varying amounts; 

 apatite very rarely. The impression given by the felspar-grains, 

 that they have been derived from a granodiorite or diorite, is 

 strengthened by the investigation of M.B., 63, a tuff on Cobbadah 

 Creek, about one mile west of the serpentine, of which, however, 

 the stratigraphical horizon is not known. It is practically a dis- 

 integrated diorite, consisting of hornblende, quartz, and minor 

 amounts of colourless augite; biotite, orthoclase, magnetite, apa- 

 tite, zircon, and pyrites, together with small fragments of cherty 

 mudstone, and andesite. There is a small amount of fine-grained 

 matrix composed of the same minerals, comminuted and decom- 

 posed. A rather similar rock occurs on Borah Creek, west of the 

 Black Mountain fault. 



The limestones of this series are a fairly constant feature, dark 

 blue in colour, with a white or greyish weathering surface, They 

 are exceedingly finely grained, and never show any sign of origi- 

 nal, organic structure. Occasionally, there are a few lighter rhom- 

 boid or rectangular patches, which stand out on weathered surfaces, 

 and are probably pseudomorphs, but the original mineral is quite 

 indeterminable. There is more or less carbonaceous matter pre- 

 sent, and sometimes finely divided quartz. 



(5) The Burin di Series consists of mudstones, tuffs, agglomer- 

 ates, and limestones, with occasional conglomerate-bands. The 

 mudstones are indistinguishable from the coarser type of the 

 Barraba Series, until the fossil-bearing horizons are reached, where 

 the rock becomes finer-grained, and darker green in colour, pro- 

 bably due to increase in the amount of chlorite and carbonaceous 

 matter. The tuffs and agglomerates, also, are identical with those 

 of the Barraba Series. A rock, the stratigraphical position of 

 which is quite uncertain, though mapped as of Burindi age, is that 



