268 THE MAEQUETTE IRON BEAKING DISTRICT. 



crystalline (juartz is present, we have the clearest evidence of two separate 

 movements, since the crystalline quartz shows undulatory extinction and 

 fracturing, sometimes according to the rectangular system. When the rocks 

 have not only been broken but interior movement has occurred tlu-oughout 

 their mass, the entering quartz has taken advantage of all of these spaces, 

 thus recemeuting the rock (PI. IX). In some cases, in the background 

 of the slate, this secondary quartz seems to be almost as plentiful as the 

 original material, occurring in little oval, comjjlex areas, in minute stringers 

 ramifying through the coarser veins, and in single individuals between the 

 fi-agmental constituents. While the cementing of the shattered rock has 

 been mainly a process of silicification, it has been indicated that a large 

 amount of oxides of iron has also entered. In some instances these oxides 

 of iron are the main constituents of the cementing material, but usually 

 they are suljordinate to the secondary quartz. Where both are present 

 theA' are not uniformly intermingled but are more or less concentrated in 

 irregular areas or l^ands. As another result of the shattering of the rocks, 

 the layers luixe been faulted in a minor degree. 



In an extreme stage of fracturing the rocks pass into genuine auto- 

 clastic rocks or reibungsbreccias. In some of these the angular fragments 

 of the slate are separated by reticulating veins of coarsely crystalline quartz, 

 finely crystalline chert or jasper, and hematite (fig. 12, p. 263, and PI. IX, 

 fio-. 1). In other cases the secondarj^ material makes a continuous ramifying 

 mass, within which are complex bands and fragments of the original slate 

 or the separated individual grains (fig. 13, p. 263, and PI. IX, fig. 2). The 

 extreme stages of brecciation more usually occur in the graywackes, the 

 filler-grained phases being more plastic and pelding more readily to pres- 

 sure, and thus developing into slates and schists. In some of the coarser 

 graywackes the relief appears to have occurred along zones of irregular width, 

 and here the grains have been loosened from one another. These zones are 

 indicated by abundant iron impregnation, and are sharply separated from 

 the layers at the sides, which have not suffered so much from movements. 



No better case is known to me of the phenomena characteristic of the 

 zone of combined fracture and flowage^ than is exhibited b}^ the Wewe 



'Principles of North American pre-Cambrian geology, by C. R. Van Hise: Sixteenth Ann. Kept' 

 U. S. Geol. Survey, Part I, 1H96, pp. 601-603, 654-656. 



