172 PROCEEDINGS OF SECTION C. 



facts which appear to have some bearing upon the question of the 

 subterranean continuity of the granitic magma. ^ 



Unfortunately, the study of the structural geology of the 

 whole region is not yet sufficiently far advanced to permit of the 

 discussion of the relation between structure and the distribution 

 of the igneous rocks in detail. However, the distribution of the 

 igneous rocks and the ore-bodies has been to some extent ascer- 

 tained, and to this matter of distribution some reference should 

 be made. 



When the attempt is made, on the assumption of the essential 

 intimate consanguinity of the acidic igneous rocks and the ore 

 deposits^, to follow the course of the Devonian intrusions of the 

 ore-bearing magma, according to the method indicated above, 

 certain striking facts concerning the distribution of mining fields, 

 granite massifs and granite porphyry intrusions arrange themselves 

 before us with singular simplicity. 



Taking the Heemskirk massif as our starting point, and 

 following the mining fields, we pass along a zone which is absolutely 

 continuous in one direction. From Heemskirk we pass to the 

 Comstock. thence to Zeehan, and on through the Fivemile, North 

 Dundas, Colebrook, Rosebery and Mt. Farrell to Granite Tor. 

 (Perhaps also the Barn Bluff field belongs to this mineralised zone.) 

 Beyond Granite Tor the Dove River and Mt. Claude mineral fields 

 can-y on the line, which perhaps extends much further still. 



The continuity is as remarkable as are the features of simi- 

 larity and relationship between different ore-bodies in the mining 

 fields mentioned. From point to point structural features vary 

 in detail. These variations are, for the most part at least, intro- 

 duced by local conditions, and have no genetic significance. 



On the other hand, restricting our attention to the distribution 

 of the acidic igneous rocks of Devonian age, we find on following 

 the same course from the Heemskirk massif, that dykes of granite 

 porphyry occur at Zeehan and North Dundas\ and that granite 

 itself outcrops massively at Granite Tor. Beyond these, and in 

 general line with them, lie the granite porphyry at the foot of 

 Bond's Peak, near the western boundary of the V.D.L. Co.'s 

 Middlesex Block, and the granite mass north of the Dove River 

 and west of Mt. Claude. Then, after a great interval, but still in 

 line, comes the aphtic and pegmatitic granite of Anderson's Creek 

 near Beaconsfield. 



This coincident lineal extension of the acidic igneous rocks 

 and mining fields appears to the author to be of the greatest 

 significance, and to imply the existence of some Hneal direction 

 of weakness in the crust. 



1 The words ' granitic magma ' are used to imply the magma from which the granite, inter alia, 

 is derived, as has been explained above. 



2 The consanguinity of the ore deposits cannot be doubted. A specimen of typical first-class 

 galena ore, with its characteristic blebs of chalcopyrite, is of constant habit, whether it be obtained 

 from Zeehan, the Fivemile, Mt. Farrell, or Mt. Claude. 



3 Apilte has been aho recorded in Zeehan, Geol. Surv. Tas., Bulletin No. 8, pp. 27-28. 

 A doubtful case of the occurrence of pegmatite has been observed to the south of Mt. Farrell, Annual 

 Report, Sec. Mines Tas., 1909, p. 83. 



