97 



there are 29,000 square miles of exposed Silurian rocks, which are almost everywhere iutersecteil by auriferous quartz 

 veins or covered in the valley by auriferous drifts, while there cannot be less than 15,000 miles of Silurian sedimentary 

 rocks concealed beneatli the Tertiary lava flows or Tertiary sedimentary rocks. In short, the older gold-bearing 

 Palaeozoic rocks extend from the western portion of the colony, in the (ilenelg Valley, to the boundary of the colony 

 on the east, a distance of over 5(M_) miles. In the eastern part of the colony the Silurian formations are in places 

 overlain by massive Devonian rocks, and in the southern Ijy Jurassic rocks ; while in the west are remains of an 

 extensive formation— the (irampians— whose age is still uncertain. With the exception of one locality in the Devonian 

 area of limited extent, these formations are not known to be auriferous. The relative areas covered by the different 

 rock masses at the surface may he estimated as under : — 



Sedimentary formations : Pala?07oic Devonian, lower, middle, and upper, 8,500 square miles ; carboniferous, 

 ■100 square miles ; Cambrian, 100 square miles ; Silurian, upper and lower, 28,300 square miles. 



Mesozoic : Triassic, -200 sipiare miles ; Jurassic, 3,684 square miles. 



Tertiary : Eocene or oligocene, miocene, pliocene, pleistocene, recent, .30,000 square miles. 



Plutonic and Igneous rocks : Basalt, 11,000 square miles ; granite, 4,000 scpiare miles; porphyries, diorites, 

 2,000 square miles. 



Bendigo Gold-field. 



The principal reefs in this field occur in the fissures produced by the arches formed by a buckling of the strata 

 into a series of folds ; or, in other words, the prominent feature of tlie field consists of numerous more or less parallel 

 axial lines, having a strike of N. 16 deg. W'., along the course of which the great mass of slate and sandstone rocks are 

 bent over into a series of anticlinals, with corresponding synclinals or troughs l)etween. The dip of the beds to the 

 east and west is about 60 feet. These axial lines or centre country do not continue horizontal for any distance, but 

 have an enddong dip or pitch. The reefs are called saddles, and thicken and diminish in size as they are traced along 



GOLD MINE BENDIGO. 



the axial lines. The eastern and western extensions are called legs. The saddles are often from 20 to 50 feet across, 

 while the legs are from 1 to 4 feet, but frequently become attenuated in depth. A succession of such saddles occurs at 

 different levels, mit generally innnediatcly below the other, but listed to one side, principally to the west. lu a limited 

 area of about 7 miles in length by 3 miles in width there are no fewer than twelve distinct lines of saddle reefs, know'u 

 as centre country. Mining operations have extended to a depth of over 3,000 feet with ijrofitable results. No less a 

 quantity than £18,009, 150 worth of gold has been w-on from this limited area, and from the Bendigo district up to date 

 £53,063,356. The deepest shafts on tlie field include : — 



Feet, 



Lansell's 180 Mine ... ... ... 3,350 



New Chum Consolidated ... ... 3,267 



Lazarus Co. ... ... .. ... .3,210 



New Chum Radway ... ... ... .3,037 



New Chum and Victoria ... ... 3,100 



Shamrock ... .. ... ... 3,000 



