1914] Lawson: Is the Boulder " Batholith" a Laccolith? 7 



tinct from laccoliths in that they are not injected, and that, whatever 

 be the nature of the bottom upon which they rest, they have not been 

 placed upon it by moving over it, but by being developed above it. 



The phenomena of intrusion may be abundantly manifest on the 

 periphery and upper surface of a batholith as exposed by erosion, 

 but these are very minor features due to stoping as described by Daly, 

 Barrell and others, to foundering of the roof, to anatexis (Seder- 

 holm), to Ut-par-lit injection, etc. These phenomena reveal the 

 method whereby the batholith makes way for itself as the melt pro- 

 ceeds, but they do not indicate that the mass as a whole has been 

 injected to its present position from some other region in the earth's 

 crust. The stresses existent in the earth's crust may become opera- 

 tive for deformation owing to the thinning of the roof, and great 

 synclinal pendants (Daly) may sink deep into the mass. Thus, 

 either by buckling or by foundering, the roof may take on an arched 

 form similar to that of a laccolith. The arching may also in part 

 be caused by an increase of volume of the region below the roof as 

 the development of the batholith proceeds ; but it is not due to uplift 

 by the insertion of a foreign mass, as in the case of a laccolith. As 

 pointed out by Termier, 12 batholiths may be distinguished in some 

 measure from injected masses by the profound character and extent 

 of the metamorphism which accompanies them : 



Pour les roehes massives, le criterium de la veritable profondeur, le 

 criterium du gisement abyssique, c 'est 1 'amplitude et 1'intensite du metamor- 

 phisme qui les entoure et qui semble emaner d'elles. Si un granite, par example, 

 n 'a autour de lui qu 'un tres petite aureole de phenomenes de contact, et de 

 phenomenes peu intenses, soyez surs que le magma de ce granite ne s'est pas 

 elabore in situ, qu'il est venu d'ailleurs, tout forme. Mais s'il est entoure 

 d'une vaste aureole de terrains tres metamorphique, et surtout s'il est enclave 

 dans une serie cristallophyllienne a laquelle il paraisse reellement lie, tenez 

 pour certain qu'il s'est forme sur place, par la fusion complete d'un eutectique, 

 alors que les terrains voisins etaient seulement semi-fluides ou meme a peine 

 ramollis.13 



Termier, with a masterly grasp of the realities of the question, 

 thus holds that the metamorphism of a laccolithic contact zone is due 

 to heat imported with the injection ; whereas the metamorphism of a 

 batholithic contact zone is due to the same heat which by fusion gen- 

 erates the batholith itself. 



i- Sur la genese des terrains cristallophylliens, Comptes Eendus, 11th Inter- 

 national Congress, Sweden, 1910. 



13 Op tit., p. 594. 



