NATURE OF BATHOLITHIC INTRUSIONS 373 



fusion — the shatter period is longer than the fusion period. In a valuable 

 paper on granites in New South Wales, Andrews has very clearly stated 

 the case. Speaking of the New England batholiths, he says: 



What we see are necessarily end reactions in the abyssal laboratories; for, 

 however powerful the youthful stage of the invasion may have been, the present 

 contact areas must represent the dying struggles only of the rising mass, since 

 at these spots the intruding massif had no longer any energy left to replace the 

 invaded rocks. Errors have often crept in, in the author's opinion, concerning 

 the idea of rock assimilation through the lack of comprehension of this fact. 

 For if weak, dying reactions give such results as one can see along the "blue 

 granite" and later acid massif contact at Bolivia ; along the Gympie slate and 

 acid granite junction at Cow Flat ; as also in the slates at Undercliffe, of what 

 tremendous potency must such action have been possessed during its maximum 

 strength, to wit, its youth or maturity.* 



The reality of the shattering is abundantly, often dramatically, evident 

 on most of the batholithic and stock contacts seen in the Boundary belt. 



The leading question remains as to the nature of the original magma 

 whose energies have effected the batholithic invasion. In the papers 

 already cited the writer has shown reasons for believing that the initial 

 magma in a complete petrogenic cycle is gabbroid, and thus basic in char- 

 acter. As so often pointed out by many authors, this magma is of such 

 wide distribution that it seems to be original in the constitution of the 

 earth. Its liquefaction, as with all plutonic magma, is doubtless conse- 

 quent upon mountain-building disturbances. Given strong liquefaction, 

 assimilation and batholithic intrusion automatically result. 



It is clear that magma may be similarly formed by the abyssal fusion 

 of sediments or schists through the rising of isogeotherms. That this of 

 itself is not the explanation of most batholiths and stocks is disproved by 

 the identity of material in contemporaneous bodies, though these respec- 

 tively cut formations of quite different chemical composition. Simple 

 fusion in place is also rendered improbable by the general sharpness of 

 batholithic and stock contacts and by the manifestly exotic character of 

 such a mass as the Castle Peak stock. 



The original magma of the Okanagan Composite batholith may, as 

 already noted, have been gabbro, now represented in the small intrusive 

 (injected?) bodies occurring in the roof pendants. The Osoyoos and 

 Eemmel granodiorites resulted from the assimilation of Paleozoic and 

 other old, relatively acid formations by the original magma. The Simil- 

 kameen batholith must also include material won from the older grano- 



*E. C. Andrews : The geology of the New England plateau, etc., Records Geological 

 Survey N. S. Wales, 1905, vol. 8, p. 19. 



