THE HEEMSKIKK MASSIF. 169 



(ii.) In a vertical direction. — With regard to the vertical 

 extensions of the concealed portions of the granite massif, still 

 greater difficulties are involved. Here we are confronted with the 

 great problem of the structural features of a great plutonic intrusion 

 — a problem to which more than one solution has been offered. 

 One of the objects of this paper is to offer a brief discussion of one 

 aspect of the question from the point of view of the student of 

 ore genesis. 



The granite massif of the Heemskirk Range would, in all 

 probability, be classified by different geologists under different 

 names, according to individual taste and usage. 



An admirable compendium of existing nomenclature has been 

 given by Professor R. A. Daly, in his paper on the " Classification 

 of Igneous Intrusive Bodies,"^ to which reference is here made on 

 several occasions. 



The igneous massif under discussion is one of which the outcrop 

 occupies a considerable area (approximately 37 square miles), 

 and which appears to descend with steeply sloping sides below the 

 surrounding rocks. Such a mass would probably be termed by 

 different geologists a stock, ^ boss,^ or batholite*; and being thus 

 named, one most important structural hypothesis would be 

 implied, viz., that with increasing depth the area occupied by the 

 igneous mass is ever increasing, and that the upper portion of the 

 igneous material rests only upon the more deeply-seated part of 

 its own mass^. 



It is to this view that the author would demur from the 

 consideration of the field relationships of the ore-bodies which are 

 beheved by him to be genetically related to the granite, as has 

 been discussed elsewhere. 



The grounds for the author's objections are largely hypo- 

 thetical, but are based upon a hypothesis constructed from the 

 evidence of actual occurrences. 



The points upon which stress is here laid are four in number : — 



(1) The ore-bodies of the region appear to constitute a 



genetically related series, of which the several types 

 are on the whole distinct, but connected by " passage- 

 types." 



(2) The ore-bodies of one type are not known to intersect 



those of another type. 



(3) The roots of the vein series appear to be, beyond all 



shadow of doubt, direct products of differentiation, 

 (i) The period of primary ore deposition appears to have 

 terminated abruptly. 

 While the cooling of the magma as a whole may well have 

 extended over a long period, the metallogenetic epoch has been, 



1 Journ. GeoL, Vol. XIII., 1905, pp. 485-508. 



2 Ibid, p. 502.. 



.3 Ibid. pp. 501, 502. 



4 Ibid. p.p. 503-505 Note : The English usage of a termination in ' — ite ' rather than' — ith* 

 is here followed for all such words. 



6 Ibid. p. 506. See also I. Barrell: "Geology of the Marvsville Mining District, Montana.'' 

 Prof. Paper No. 57. U.S.A. GeoL Surv., 1907, p. 168, and E. Suess : "The Face of the Earth," 

 Vol. IV., p. 551. 



