254 



has been so complete in many instances that what looks in 

 general form like a sedimentary rock, shows, on fracture, com- 

 plete crystalline structure. The beds contain much ilme- 

 nite, which is often sporadically developed, and generally in 

 association with quartz. These granitoid beds are a leading 

 feature in the Inman Valley exposures, and are of great ex- 

 tent. 



The unconformity of the two series is determined upon 

 the following considerations : — 



A The great discordance in structural features. 



(a) The underlying beds are to a large degree, crystal- 

 line, interpenetrating, and intrusive, inducing 

 marked contact metamorphism in the sedimentary 

 beds of the same series. 



(h) The overlying grits and conglomerate are as clearly 

 clastic in origin, and in no instance was it ob- 

 served, in either the Aldgate or Grey Spur sec- 

 tions, that the aplitic veins pass over the line of 

 junction and penetrate the upper series. In other 

 localities, however, veins of pegmatite penetrate 

 the Cambrian grits. 



(c) The Pre-Cambrian beds are highly foliated, whilst 



the newer series, in the localities now more par- 

 ticularly referred to, gives no distinct evidence of 

 foliation. 



(d ) The gritty particles forming the matrices of the upper 



beds give proof that they are derived, whilst the 

 arkose character of these- grits points to the dis- 

 integration of the underlying granitoid rocks as 

 the source of the material. 



( (' ) The occurrence of ilmenite in both series of beds is a 

 characteristic feature ; only, in the Pre-Cambrian 

 it is a primary constituent, whilst in the Cambrian 

 grits and conglomerates it is usually laid down on 

 distinct planes of current deposition, showing its 

 secondary origin. The quartz pebbles in the con- 

 glomerate, which have been derived from the older 

 beds, frequently contain ilmenite crystals or plates. 

 B The sir((f)(/r(i'phic<d loivonfontui ij. 



(f) There is a distinct discordance shown along the plane 

 of junction, the Pre-Cambrian having usually a 

 much higher angle of dip (foliation) than the over- 

 lying beds. 



BarosiSft. At Williamstown, slates (probably the lower 

 phyllites) outcrop in Victoria Creek, and are nearly vertical 



