Yol. 55.] PALEOZOIC RA.DIOLAKIAN EOOKS IN IfEW SOUTH WALES. 33 



addition of the silica from the tuffs, it is evident that the silicifi- 

 cation has been accompanied by a replacement of the bases. 



One of us (T. W. E. David) has already emphasized the fact that at 

 the Jenolan Caves the black cherts, fall of raiiolarian casts, form a 

 persistent selvage to the intrusive basic dykes of that neighbourhood.^ 



Y. Microscopic Characters. 

 {a) The Radiolarian Eocks. 



Slide No. 240 (1). Radio] arian limestone with tuff-fragments, 

 Tam worth Common. A calcareous, dark bluish-grey rock weathering 

 into a deep chocolate-brown pulverulent crust, with greenish patches 

 about 12 X 6 mm. across. When etched with hydrochloric acid, tbe 

 bulk of the rock is seen to be composed of insoluble material, some 

 of which is silica. By reflected light the colour of this is pale 

 citron-greenish-grey to very pale neutral tint or pale bluish-grey, 

 resembling the opalescence of water with a few drops of milk in it. 



No primary quartz is present. The outlines of the pardcles are 

 very irregular, with the exception of the radiolarian casts, which 

 are spherical. 



The radiolarian tests mostly have their original substance pre- 

 served, and are infilled with calcite. The medullary tests have 

 suffered much less from decomposition than the cortical tests. 

 These radiolaria are from 0'125 to O'l mm. in diameter. 



Slide No. 244 (2). A very homogeneous calcareous radiolarian 

 rock, showing black dusty bands at intervals of about 3 to 6 mm. 

 parallel to the planes of bedding (?). 



Under the microscope the black material is seen to belong to 

 more or less perfect tests of radiolaria, the spaces between the 

 meshes of the tests being filled in with translucent calcite. Most 

 of the tests are so broken down as to have had almost all of their 

 original structure obliterated, except their bare outline and the 

 position of the largest of their spines. A few tests, however, are 

 remarkably well preserved, but many are represented simply by 

 translucent internal casts composed of calcite. In diameter these 

 casts vary from about O'l to 0*15 mm. 



Slide No. 251 (j3). — Eadiolarian limestone No. 5, Tamworth 

 Common. Eock calcareous ; a few fragments of a chiastolitic rock are 

 present ; the fragments measure O'o mm. in diameter. The bulk of 

 the rock is calcite, with a pale greenish mineral, weathered reddish- 

 brown in places, and sometimes feebly dichroic and fibrous. This 

 appears to have taken possession (in one case) of the interior of a 

 radiolarian test. Small patches of chalcedonic quartz, forming casts 

 of radiolaria, are scattered through the calcareous groundmass. It 

 looks like an altered radiolarian rock, with chips of chiastolitic (?) 

 claystone. 



Slide No. 563, Eth. (4789).— Tamworth, from clay-shales at the 

 serpentine-quarry, about 30 chains north of Patterson's house. 

 ^ Proc. Linn. Soc. N.S.W. ser. 2, vol. xi (1896) p. 5(55. 



Q. J. G. S. No. 217. D 



