534 THE MAEQUETTB lEON-BEAKl^'G DISTRICT. 



condition at the time that tlie conglomerate was hiid down, that it supplied 

 a large part of the materials out of which the conglomerate was built, and 

 furnished the basement upon which it was deposited. In short, the contact 

 is one of erosion, the conglomerate is a basal conglomerate, and the facts 

 indicate an important time-break at its base. 



At the other locality, in sec. 7, T. 47 N., R. 30 W. (Atlas Sheet YII), a 

 short distance south of the Magnetic mine, the evidence is not so clear. 

 Between the undoubted granite and the iron-bearing member is a consider- 

 able interval occupied by banded gneisses and mica-schists, which certainly 

 include part of the horizon of the lower quartzite, but how much it is 

 impossible to determine. Some of the gneisses and schists have evidently 

 been derived in place from the gi-anite, through shearing parallel to the 

 contact; others seem clearly to be metamorphosed sediments in which it is 

 possible to detect here and there traces of the larger quartz pebbles. But 

 between them there is a considerable interval of somewhat similar gneisses 

 and schists the origin of which is wholly indeterminate. The facts here 

 are quite in harmony with the view that the contact is an erosion contact, 

 although they do not give it direct support. 



The two contacts, therefore, at which direct juxtaposition is found 

 justify the conclusion that the relations between the Lower Marquette series 

 and the Archean are those of an erosion unconformity, that the Archean 

 in its present form is the older, and that a considerable interval of time 

 elapsed between the formation of the Archean rocks and the deposition of 

 the Ajibik quartzite. 



The lithological character of the Ajibik quartzite, wherever it is found, 

 must be taken as corroborating this conclusion. It will be rememliered 

 that this rock is composed of quartz with variable proportions of light- 

 colored mica, muscovite, or sericite as essential constituents. These micas 

 hiwe proljably been derived from the alteration of original orthoclase or 

 microcline, feldspars characteristic of the Archean granites, of which the 

 quartzite otherwise shows now no traces. The quartzite was then probably 

 a feldspathic sandstone, composed of granitic debris such as the breaking 

 down of the adjacent underlying granite woidd unquestionably furnish. 

 The persistence of its lithological character and the fact that it is always 



