138 E. 0. Trale: 



"warping of overlying areas be regarded, as tlie most favourable ex- 

 planation of the mechanism of such an important petrogenic phase 

 in earth history. 



The Relation of the Dyhe Bocks and Qiun-tz Reefs to Structure 

 and Earth Movements. 



It has long been recognised in Victoria that many of the impor- 

 tant gold-bearing reefs can be grouped along certain more or less 

 parallel zones, with a northerly trend, and separated by other belts 

 of non-productive reefs or marked by the absence of reefs alto- 

 gether. Most of the Victorian reefs (excepting the Bendigo and 

 Castlemaine fields) occupy definite fissures, or are associated with 

 igneous dykes which have intruded fracture lines. The bearing of 

 these occurrences in general is northerly, parallel with axial lines 

 of folding. 



The age of the great reef formation is generally believed to have 

 been Devonian, and genetically associated with the granitic intru- 

 sions of that epoch. 



One belt in particular, is worthy of mention, illustrating very 

 well the features above mentioned; na-mely, the Walhalla-Woods 

 Point Zone. Tlie prevalence of dykes, frequently of a diorite type, 

 and auriferous reefs along this zone, is in contrast to their absence 

 in the country to the west and east. Other such instances might be 

 mentioned. There are also non-auriferous zones, where fractures, 

 faults or dykes are common, about which, however, little is known 

 with regard to their age and distribution. Many of these may not 

 be Palaeozoic, and tliese are therefore not included in the present 

 discussi'on. 



It would appear from the consideration of the above that one 

 phase of the great Devonian tectonic and igneous disturbance 

 found expression in tlie development of lines of fracture, with a 

 definite northerly trend along certain zones, and their infilling 

 with igneous dykes and quartz reefs. The geological study of these 

 areas has so far not revealed anything to suggest that these frac- 

 ture lines can be regarded as planes of great differential movement 

 on either side of which important earth blocks or segments were dis- 

 located. They would appear ratlier to indicate zones of tension 

 due to crust al adjustment, accompanying the folding and batho- 

 lithic intrusion/ of that period. 



The Fracture Line of the Snoiry R^'ver Porphyries. 



As indicated previously, this zone is the only one where the occur- 

 rence of certain igneous rocks other than dykes of the Devonian 



