304 Canadian Record of Science. 



bands, generally forming with the latter an angle of about 

 60° (see fig. 8). In another place nearly a quarter of a 

 mile distant, the banding was horizontal and the foliation 

 of the bisilicates perpendicular. In these cases both the 

 original rude banding, the result of movements in a 

 heterogeneous magma, as well as the subsequent foliation 

 of the bisilicate .masses, resulting from pressure, are to be 

 observed in the same exposures. 



In a large area covered by forest, such as this, the 

 actual line of contact cannot usually be seen, but where 

 they can be observed, both rocks are cut through by peg- 

 matite dykes; indeed, the gneiss itself often appears to 

 send out an arm-like extension into the anorthosite as if 

 it were an intensive rock and had not been broken 

 through by the anorthosite. As it has been shown that 

 the granulation of the anorthosite in all probability 

 originated when the rock was still very hot, it is quite 

 possible that these arm-like offshoots are portions of the 

 gneiss which were pressed into cracks in the anorthosite 

 while the latter was in a more or less plastic condition. 

 This explanation is supported by- the remarkable fact 

 which is observed in hundreds of cases in different parts 

 of the Laurentian, that wherever orthoclase gneiss and 

 amphibolite alternate with one another, and the whole 

 mass is squeezed, the bands of amphibolite without excep- 

 tion break apart into fragments, between which the 

 gneiss is pressed. A species of breccia is thus formed, 

 which may be followed in the direction of the strike into 

 a regular series of alternating and undisturbed bands. 

 Under the influence of pressure, probably accompanied by 

 intense heat, the basic rock is always more, brittle than 

 the acid one. 



The gneiss may indeed, often result from a later erup- 

 tion, since it is almost massive, as already mentioned, and 

 belongs in all probability to the lower or Ottawa gneiss, 

 in which much intrusive material undoubtedly exists. 



