Geology of the Diamond Creek Area. 331 



been ])irke<l up where it crosses the Maroondah aqueduct in the 

 north of the area. The railway section shows that near tiie axis 

 tlie fold is extremely crumpled and crushed. Small thrust faults 

 having displacements of three or four feet are common. No quartz 

 reefs occur near bv, and this is what we might expect. In general 

 it is only in places where the rocks have fractured by tension as 

 near the anticlinal axes that fissures have formed through which 

 solutions have reached the surface. Following Gregory and Jutson 

 it is proposed to call the above fold the Greensborough syncline. 

 The western limb of this syncline consists of fairly steep, dijiping 

 beds, and near the Plenty River it passes into a sharp anticlinal 

 flexure. The anticlinal axis is not symmetrical having a dip to 

 the east of about 70 deg. In a section in Dry Creek an acid dyke occurs 

 i-ight on the axis. Going further east from here along the east 

 iind west bend of the Plenty River, two or three minor folds occur 

 fairly close to one another. The Templestowe anticline is, how- 

 ■ever, the axis with which we are most directly concerned. Jutson^ 

 has traced this fold for nine miles south of the northern boundary' 

 of the parish of Nillumbik. The wi-iter has traced it still further 

 north to near Hurst's bridge, that is, for about three miles further 

 north. The Avestern limb of the fold, as Jutson has pointed out, is 

 very greatly contorted and fractured. This is very well exemplified 

 at and near the Diamond Creek mine. The silurian sediments 

 throughout the area are well jointed, but near the above-mentioned 

 anticline, rectangular jointing is sometimes so Avell developed that 

 it is almost impossible to di.stingui.sh bedding from joint planes. 

 This is well illustrated in cuttings in the recently-opened railway 

 to Hurst's bridge. Another interesting feature are the numei'ous 

 bedded and nearly vertical joint plane reefs in close proximity to 

 the axial lines, especially the anticlines. It appears clear, there- 

 fore, that the pressure near the anticlinal axes during folding was 

 tensional, and led to the formation of fractures and fissures 

 through which mineral-bearing solutions have reached the surface, 

 "while the pressure in the synclines was compressional rather 

 than tensional, as is shown by the case of the Greensborough 

 syncline above mentioned, and hence no passages or outlets for 

 solutions from below occurred. Hence the reason for the localisa- 

 tion of the mining belts to the anticlines.^ such as Warrandyte and 

 Diamond Creek, is apparent. 



Associated with the Diamond Creek cTyke there occurs a zone of 

 brecciation which will be dealt with in detail later. 



1 Jutson. 1), p. .5'22. 



2 The proximity of acid dykes to the .inticliiies near Warrandyte, Diamond ("reek, Dry Creek 

 and Templestowe furtlier illustrates this point. 



19a 



