200 THE MAKQUETTE lUON BEARING DISTRICT. 



of l)i()tite Hnkcs that ;iro l)eiit to coMt'orin witli tlic outlines of tlio crvstal. 

 Phenomena of the same kind are met with in so many sections that the 

 belief in a (Ivnamic origin for the foliation of the schists is irresistible. 

 The scllistosit^' was imposed npon the rocks prior to the alteration of the 

 feldspar in some cases, and in other cases it was produced sid)sequent to 

 this alteration This is easily accounted for on the supposition that the 

 feldspars were partially altercid before the I'ocks containing- them were 

 mashed, and that the alteration continued after tlie mashing. While in some 

 cases tlie alteration product^^ are arranged as in a fine-grained schist, with 

 the schistositv planes i>arallel to the elongation of the (piartzes and to the 

 longer axes of the large biotite flakes, in other instances no such general 

 an-angement is noticeable. In these cases the small biotite flakes in the 

 secondar)^ aggregate lie in all azimutlis, except where tlieir positions have 

 been determined by the structure of the mineral from which they were 

 derived. In the section of rock. No. 19034, for example, the tiny biotites 

 are often f()und in two series of lines crossing each other approximately 

 at right angles, having been formed apparently in the cleavage cracks of 

 feldspars. 



COMPOSITIIIN' AXll iiliUa.V. 



The micaceous schists are so much altered that the nature of the 

 original rock from which they were formed is not known. The existence 

 of large cr\-sta]s of orthoclase with the outlines of phenocrysts in the midst 

 of a cataclastic groundmass would seem to indicate that the original rock 

 was an aciil porphyry, but these are so rare that any broad generalization 

 based upon tlieir presence must be of doui)tful value. It is true that no 

 sedimentary grains have been discovered in any of the thin sections, and 

 this fact would seem to point to a similar conclusion. But all the rocks 

 have been so greatly altered in structure l)y the changes thev have luider- 

 gone that it would lie surprising if any evidence of their original structure 

 were discoverable. 



From the evidence of the microscope, all that can be said i-egarding 

 the origin of the schists is that they are more })robably igneous rocks thau 

 sedimentary ones. Their banding may be accounted for on the supposition 

 that they occurred as flows of lava, for, though they are as evenly banded 



