610 GREAT SERPkN TINE-BELT OF NEW SOUTH WALES^ V., 



more finely gTanular. Tlie chief distinction, however, lies in the 

 greater abundance of quartz and acid felspar in the newer rocks, 

 fragments of cryptocrystalline and trachytic keratophyre being 

 very common. In addition to this, there is an abundance of purely 

 keratophyric material, which forms the white interlaminations in 

 the claystones; these vary in thickness from some yards down to 

 fractions of a millimetre. Sometimes they have a flat lower side 

 when they have fallen on to partially consolidated clay, or the 

 underside may be indented where the falling grains sank into soft 

 silt. The upper side is quite irregular in both cases (see Plate 

 liii., fig. 7).' Such interstratified tuffs may contain radiol aria 

 or plant stems. Intrusions of keratophyric tuff into the 

 sediments are frequently observable under the microscope, 

 a particularly clear instance being that shown in Plate 

 liii., fig. 8. Fig. 9 of the same plate illustrates a clearly clastic 

 rock, which is similar in all respects to the intrusive material in 

 the specimen shown in Fig. 8. 



The general character of the Upper Middle Devonian 

 and Upper Devonian pyroclastic rocks has been described 

 thus: — "At some depth below the surface the colour of the tuff 

 is greenish-grey, weathering to yellowish-brown or lighter grey at 

 the surface, and thus contrasting strongly with the darker clay- 

 stones. A chemical analysis of the tuff will be found on p. 602. 

 Mr. Card describes them as felsite-tuffs, with numerous fragments 

 of cryptocrystalline felsite (Keratophyre, W.N.B.) entangled 

 in the holocrystalline or microcrystalline groundmass. The 

 latter is composed of broken or corroded crystals of plagio- 

 clase, orthoclase, quartz, and augite, with occasionally horn- 

 blende, and rarely sphene" (titanomorphite, W.N.B. ). "Small 

 crystals of iron pyrites are diumerous and grains of titani- 

 ferous iron sometimes occur; small and large inclusions of 

 radiolarian rocks abound. "(9). The fragments of radiolarian 

 rock in the tuff are often very rounded (see Text-fig. 10), and there 

 is some alteration of the tuff about them. Numerous instances 

 occur in which the inclusion is ringed around by a pinkish-white 

 zone, which is very distinct macroscopically. Under the micro- 



