BY W. N. BENSON. 133 



amount and decrease in grainsize of the magnetite; and by the 

 substitution of a very slaggy for an amygdaloidal habit. The 

 change from keratophyre into magnetite-keratophyre is a more 

 complex one, and is discussed at length in the sequel. 



North and south of Folly Creek, near the serpentine, there are 

 small masses of spilitic magnetite-keratophyre, which seem to be 

 intrusive into the adjacent sediments. No unusual tectonic 

 features appear in their neighbourhood. Here and there through- 

 out the district are little patches of spilite, richer than usual in 

 magnetite, and showing some approach to the character of mag- 

 netite-keratophyres. These, however, are of rare and limited 

 occurrence only. 



The main region of development of the purely keratophyric 

 type of rocks lies north-west of Bowling Alley Point in the 

 region between Hyde's and Cope's Creeks. About a mile due 

 west of the small infaulted area of Permo-Carboniferous rocks, is 

 what may be termed the Hyde's Creek Complex. It forms a 

 small ridge, running back from the creek. Fig. 4 is a map of the 

 occurrence. The normal strike of the region is that seen to the 

 north-east of the figure, namely, N.N.W.-S.S.E. The strata 

 following this strike are steeply inclined cherts and agglomerates 

 or breccias. The strike warps round from N.N.W. to W.N.W. 

 A fault cuts almost perpendicularly across this, and south of the 

 fault lies an area, the strike of which swings from N.E. to E.N.E. 

 The line of fault is marked by a series of masses of jasper, not of 

 the usual red homogeneous character, but more clearly a secondary 

 vein-like and vesicular rock, with quartz and chalcedony and 

 crystalline haematite ; the last is present as a finely divided 

 colouring matter, as crystals in druses, and in veinlets through 

 brecciated jasper. Where the jaspers cease, there continue zones 

 of red jasperised radio] arian chert. Microscopical sections of 

 these clearly show the metasomatiq effect of ferruginous siliceous 

 solutions. 



Intrusions of igneous rock occur both north and south of the 

 fault-line. At the southern end of the hillock is a complex of 

 keratophyre and magnetite-keratophyre as shown. No actual 

 contact with the chert has been seen, but the intrusive nature of 



