170 PROCEEDINGS OF SECTION C. 



according to the views of the author, of relatively short duration — 

 beginning when consolidation was already far advanced, and 

 itself marking the utter termination of consolidation. 



If the batholitic structure exists, it is difficult to believe that 

 existing facts of occurrence could have resulted. For then it 

 appears probable that consolidation would have extended over a 

 much longer period, and that from time to time the derivatives of 

 successively deeper portions of the magma would have been 

 extruded. The result would undoubtedly be a marked inter- 

 section of the older veins characteristic of one zone by younger 

 veins characteristic of a higher zone, as the source of the vein 

 matter became deeper and deeper, through consolidation of the 

 magma. 



It appears to the author impossible, in view of the field 

 ■evidence, to admit the alternative view of a batholitic mass in which 

 the mineralisers and metallic ingredients have floated to the top 

 and there collected in a reservoir, so that the metallogenetic epoch 

 ■closed, not with the complete consolidation of the magma, but 

 with the exhaustion of the reservoir of mineralisers and metals. 

 The observed facts point to a general, if irregular, distribution of 

 metallic ingredients and mineralisers throughout the whole mass 

 ■of the magma, or at least through portions which have always 

 possessed very different altitudes since they reached their mise 

 ten place. 



We therefore appear compelled to adopt the view that the 

 mass of the magma is limited. The substructure of the Heemskirk 

 Range is not an ever-expanding mass of granite which is connected 

 •with the deeper portions of the earth. When once the limited 

 mass of igneous material has passed into the completely solid state, 

 all connection with the abyssal region has been effectively sealed 

 inp. This view implies the necessity for a very definite bottom to 

 1he greater part of Heemskirk massif, above which lie the magmatic 

 foci whence the ore deposits have been expelled. 



What then are we to call the Heemskirk massif? The only 

 term applicable appears to be that invented by Professor Daly — 

 chonolite. The definition of a chonolite, according to the creator 

 of the term, is^ : — 



" An igneous body (a) injected into dislocated rock of any 



kind, stratified or not ; (b) of shape and relations 



irregular in the sense that they are not those of a true 



dyke, vein, sheet, laccolite, bysmalite or neck ; and 



(c) composed of magma either passively squeezed into 



a subterranean or orogenic chamber or actively forcing 



apart the country rocks." 



The form of the particular mass under consideration is probably 



extremely complex. The visible outcrop resembles that of a 



batholite or stock ; but, as has been indicated above, it is highly 



probable that this particular outcrop is that of a mass possessing 



some of the features of an irregular transgressive laccolite. ^ 



1 Loc. cit. supra., p. 499. 



2 Vide A. Harker : "The Natural History of Igneous Rocks," p. 68, fig. 11. 



