128 GREAT SERPENTINE BELT OF NEW SOUTH WALES, iv., 



may be a repetition of the first zone, though this does not 

 seem probable at present. Near the entrance to the gorge is 

 exposed the mass of chert and spilite shown in Fig. 2 A. This is 

 the only instance in which doubt may exist as to the intrusive 

 nature of the pillowy rock. The manner in which the banding in 

 the chert bends in and out sympathetically with the boundaries 

 of the lava-pillows, may indicate that they were deposited on a 

 pillowy surface. On the other hand, the upper mass of lava has 

 transgressive boundaries against the chert. It is not pillowy 

 where it is in contact with the chert, but the structure becomes 

 observable about thirty feet above the chert. The upper mass 

 may be a surface-flow which has broken up the lines of bedding 

 of the clays over which it flowed, but the section does not pre- 

 clude the possibility that both the upper and lower masses of 

 igneous rock were intrusive into soft clays, crumpling, or break- 

 ing through their lines of bedding as they went. Exposures of 

 chert and spilite observed higher up the gorge clearly exemplify 

 the second alternative. Indeed, there does not seem any other 

 explanation possible for the features illustrated in rigs.2B and 

 .20. These narrow bands of chert lie in a great thickness of 

 pillow-lava, probably four or five hundred feet (screes and tangling 

 brushwood prevent more exact measurement). The pillows may 

 be as much as eight feet in diameter, and are just like those 

 occurring in Happy Valley. Not infrequently they are quite 

 free from vesicles. In between the pillows is often a very fine- 

 grained rock which looks like chert, but which the microscope 

 proves to be made up of quartz, epidote and a little actinolite; 

 the same minerals, less finely crystallised, form the usual bands 

 separating the pillows. As in Happy Valley, there is no radio- 

 larian chert between the pillows, nor do they show the strongly 

 marked radial contraction-cracks that are sometimes seen in 

 similar rocks in other parts of the world. There are associated 

 massive intrusive dolerites quite indistinguishable, in hand-speci- 

 men, from the rock in the centre of the pillows (though under the 

 microscope they may appear less variolitic), and it is often diflS- 

 cult to determine whether there is a passage from the pillowy 

 rock into the massive dolerite, or whether there is a definite 

 boundary between them. 



