700 CLARENCE N. FENNER 



important results have been accomplished through their agency. 

 We must suppose that these gases will exert a fluxing or solvent 

 action upon the minerals of the walls, so that some fraction of them 

 shall form a solution with these minerals, giving rise to a sort of 

 secondary magma within the walls. 



Moreover, during the advance of streams of magma between 

 layers of rock, such as is characteristic of lit-par-lit injection, it 

 seems almost inevitable that by contact with the cooler walls a 

 portion of their load of dissolved material should be deposited. 

 Thus the solutions ahead would become progressively more dilute, 

 but with the rise of temperature ultimately produced in the walls by 

 the stores of heat imparted to them by a number of closely adjacent 

 streams of magmatic solution unchanged magma would finally 

 enter among the layers and carry farther toward a conclusion the 

 processes of transformation initiated by the solutions in advance. 



By whatever means a differentiation of the magma-streams is 

 effected, the advance of the magma into the wall-rock would be 

 attended by phenomena of various sorts, such as impregnation of 

 the walls, solution and removal of some of the components of the 

 wall-rock, and reactions with the minerals with which the solution 

 came into contact. 



When the chemical nature of the wall-rock diff'ers greatly from 

 that of the magma the reactions between the two might be expected 

 to effect striking results. Limestones seem especially fitted to 

 react with the magma, but other rocks may participate in a like 

 manner. For this reason it may not be possible to decide what 

 the nature of the original rock has been, as was pointed out in 

 considering the character of the strata invaded by the magma in 

 the New Jersey example. Instances of the extreme effect pro- 

 duced by such reactions were found by Adams and Barlow"^ in the 

 Haliburton-Bancroft area. A passage in their publication refers to 

 a certain contact of a granite batholith with the limestone wall-rock, 

 and reads as follows : 



.... The limestone bands fade away imperceptibly into the amphibolite, 

 the latter being undoubtedly produced by the alteration of the Hmestone. These 

 rocks are invaded by the granite, traversing them in apophyses which swarm 



'Adams and Barlow, "Geology of the Haliburton and Bancroft Areas," Memoir 

 No. 6, Canadian Geological Survey (1910), p. loi. 



