174 PROCEEDINGS OF SECTION C. 



Middlesex, it is interesting to observe that the outcrop of granite 

 at the Meredith Range and Heazlewood, the granite porphyry 

 at Mt. Bischoff, the outcrop of granite on the Blyth River to the 

 east of the V.D.L. Co.'s Hampshire Hills Block, and again that of 

 the Dial Range, are disposed in a zone which is approximately 

 parallel to the former. The further investigation of this zone 

 cannot at present be made. 



There remains the North Pieman massif, which is not a pro- 

 minent one, its surface being barely exposed by the total effect of 

 successive cycles of denudation. With it are to be grouped the 

 dykes on the coast line to the south of the Pieman Heads. The 

 relationship of this massif to that of Heemskirk and that of the 

 Meredith Range cannot be said to have been definitely recognised 

 in any particular. 



Whether the Meredith Range massif has any connection with 

 the Heemskirk-Middlesex zone remains to be proved. Should 

 the hypothesis here put forward be sound in principle, it will be 

 of interest to investigate in the future the already recognised zone of 

 intrusion, marked by the basic rocks which extend from the Cole- 

 brook Hill towards the Parson's Hood, for signs of the acidic 

 magma. 



V. — Conclusion. 



From the several considerations discussed, the author would 

 affirm that the relationships of the Heemskirk massif to its 

 immediately surrounding rocks, to the associated dykes and ore- 

 bodies, to certain other similar massifs and other ore-bodies, and 

 to certain of the main structural features of Tasmania are approxi- 

 mately known. These relationships may be briefly summed 

 up as follows : — 



(1) The relationship to the surroitnding rocks. — The granite 

 outcrop is that of a massive transgressive intrusion of irregular 

 form, but limited mass — that is to say, of a " chonolite " or 

 irregular transgressive laccolite. 



(2) The relationship to associated dykes and ore-bodies. — ^The 

 granite is one of the products of the consolidation of a magma 

 which gave birth, during its passage into the solid state, to a definite 

 succession of fractional parts, all of which taken together constituted 

 the essence of the magma at the time of irruption. Of these 

 fractional parts the granite is the greatest in mass. The ore- 

 bodies formed within the limits or in the immediate neighbourhood 

 of the massif, are the latest-born products of the parent magma, and 

 are zonally disposed with regard to the granite. The temperature 

 of the granite at the period of ore-deposition has exerted a potent 

 controlling influence upon this zonal distribution of metallic ores. 



(3) The relationship toother similar massifs and otiier ore-bodies. — 

 The Heemskirk massif, with its apophyses and cognate dykes and 

 veins, is genetically related to the similar invading materials which 

 made their irruption into many parts of Tasmania shortly after 

 the close of the Silurian period. They are most directly related 



