592 GREAT SERPENTINE BELT OF NEW SOUTH WALES, v., 



feet, with a bank of gravel and boulders in the centre of the 

 valley ten feet high above this. (8ee Text-fig. 14). 



Alluvium of the Flood-plain. 



The broad flood -plain of the two rivers is covered with a soft, 

 black loam, of great agricultural value. In places, it is more 

 than a mile wide, and is of varying depth, generally ten to fifteen 

 feet. This is the depth of the soil by the railway-viaduct. 



Petrology. 



The following- notes are based upon a study of about two 

 hundred thin slices of rocks from the Tamworth district, of which 

 seventy came from the collections of the New South Wales Geolo- 

 gical Survey, and of the University, and were those used by 

 Messrs. David, Pittman, and Card, in the preparation of the pre- 

 vious paper on this area. Attention has been devoted chiefly to 

 the igneous rocks; the sedimentary and metamorphic rocks show a 

 nmch smaller range of interesting features. The chronological 

 order has been followed as far as possible in the sequel. 



Eastern Series. 



The basic rocks of the Eastern Series are spilites, vitro- 

 phyres, and hornblende-schists, the product of the contact- 

 metamorphism of the spilites. The spilite, which crosses the 

 head of Spring Gully, south of Portion 189, Nemiugha, has a 

 poorly developed ellipsoidal habit, is massive or slightly sheared, 

 and of fine grain-size. It has a well marked subvariolitic structure 

 (1354). The felspar has been largely changed to epidote, the 

 remainder is glassy, and frequently untwinned; it is probably 

 albite. The pyroxene is changed to chlorite, or remains quite 

 fresh. It is a colourless diopside. Magnetite-crystals occur iu 

 abundance. There are small veins of epidote, quartz and chlorite. 

 A completely epidotised rock was found by Mr. Aurousseau, as a 

 pebble in Spring Creek, doubtless derived from the Eastern Series. 

 It is very like the Pre-Cambrian spilitic dolerite, from Tayvallich, 



