GEOLOGY OF NUNDLE DISTRICT. 101 



fragments up to half an inch in diameter, and rarely casts of radio- 

 laria. Above this is an horizon in which coral limestone is fre- 

 quently developed, containing a Middle Devonian fauna. The fol- 

 lowing forms determined by Mr. W. S. Dun were collected from 

 this horizon : Favosites muUitabulata, F. salebrosa, and a dendroid 

 species ; Diphiphyllum porteri, Heliolites porosa ; Alveolites ; Lito- 

 phyllum Konincki, ; Atrypa. 



This calcareous belt is made up of brecciated red marble, white 

 marble, silicified blue limestone, or very impure tuffaceous limestone. 

 Frequently its place is occupied by a black, seemingly vesicular, 

 rock in the cavities of which coral fossils may occur. Microscopically 

 the rock suggests a rapidly-chilled lava flow, and is full of skeleton 

 crystals of magnetite and other minerals. The calcareous rocks are 

 not confined to this one horizon, but may occur both above and 

 below it. There are also occasionally thin limestone lenses in the 

 banded cherts. The upper portion of the Bowling Alley Series 

 is made up of a succession of tuffs and radiolarian cherts, with slate 

 layers and shale bands in which Lepidendron australe occurs. They 

 pass without unconformity upwards into the Nundle Series. In 

 these, however, the dips are less steep, and sometimes the beds are 

 almost horizontal. The series is composed of a succession of fine- 

 grained andesitic tuffs and soft laminated clay-shales and mud- 

 stones. In places these may become cherty ; elsewhere there are 

 bands of conglomerate containing granitic pebbles, and frequently 

 there are thin limestone lenses. 



During the Devonian period of sedimentation volcanic activity 

 was pronounced ; vast quantities of ash were ejected, and probably 

 lava flows were frequent. The products of this activity must be 

 in the aggregate over a thousand feet in thickness. In chemical 

 nature it is chiefly andesitic, though occasionally felsitic. During 

 the close of the Devonian period orogenetic movements began, 

 accompanied by great earth folding, the axis of the folding being 

 about N. 20° W. and S. 20°E., and the force was directed from the 

 east. It is probable that in this folding the Woolomin Series was 

 repeated by isoclinal folding and thrust up over the Bowling Alley 

 Series. Along this strike fault plane ultrabasic rocks were intruded ; 

 they thus occur at an almost definite horizon in the sedimentary 

 series, but at the same time there are a few minor intrusions both 

 in the Woolomin and Bowling Alley Series. Near Hanging Rock the 

 serpentines leave the junction line of Woolomin and Bowling Alley 

 Series and intrude the lower portion of the latter. The rocks 

 developed are oUvine and pyroxene serpentines of various types, which 

 may have become siUcified or carbonated, and more or less saussuri- 

 tised gabbros. Following this intrusion came the diabases. These 

 form exceedingly irregular masses, and within the area studied are 

 confined to the Bowling Alley Series. They vary considerably in 

 texture and grain size and contain pegmatoid veins. Pjo-ites is a 

 common accessory. Closely connected with these intrusions was 

 the formation of the numerous quartz veins, which contained origi- 

 nally most of the gold in the district. With these there is sometimes 



