THE LOWER HURONIAN. 331 



there is a series of interbedded jaspers, cherts, iron ore, carbonate-bearing 

 slates, and normal slates and graywackes, having a width of about 50 feet. 

 The dips on this exposure are all to the south. No dips were taken which 

 were less than 55°, and most commonly they were 60°. On the southeast 

 side of the bay northeast of this point, there is an excellent exposure which 

 gives a cross section of the iron formation. The best exposures in this 

 area, however, are those on the range of hills crossed by the portage from 

 Agawa Lake into This Mans Lake. On the hill immediately north of 

 the west end of the portage there is well exposed a series of narrow 

 interlaminated bands of jasper, iron oxide, chiefly magnetite and chert, with 

 some slaty bands. Between these, and interlaminated with them, there 

 occurs well-banded and thinly laminated gray slate. These interbanded 

 belts of slates and iron formation proper continue to outcrop along the 

 hill to the east. From this hill a north-south traverse was made, and here 

 it was found that the youngest rock, that which occupies the center of the 

 area, is a gray sericitic slate having a width of about 75 feet, and striking 

 about N. 45° E. On each side of this — that is, both north and south of it — 

 there occurs the iron formation, consisting of a complex of three belts of the 

 iron formation proper, and two intervening belts of slate. The approximate 

 width of the complex on each side of the central belt of slates is 50 feet. 

 North and south of the iron formation there is a considerable width of gray 

 slates, which are in their turn succeeded by interbedded graywackes and 

 slates, and, finally, north and south of these sediments comes the Ely green- 

 stone as basement. This greenstone was not seen at just this locality, but 

 its relation to the sediments was obtained on the strike of these beds to the 

 west, and but a short distance away from this point. From the repetition 

 of these various rocks it is clear that the structvire at this place is 

 synclinal. The greenstones on the south and north represent the oldest 

 rocks, the younger sediments occurring above them toward the center 

 of the syncline. The structure of the rocks evidently detei'mined the 

 topograph}" in this region. The lakes lie in the center of and at the bottom 

 of this slate syncline. It is true that at this place the iron formation does 

 not lie absolutely at the base of the slates, since there are some slates 

 between it and the conglomerate. Nevertheless it occui-s essentially at the 

 base of the formation. This was an area in which, as is shown by the 

 rocks, the conditions of deposition were rapidly changing. Slates were at 



