Ill A. P.COLEMAN — DPPEB AND LOWER HURONIAN IN ONTARIO 



instance, however, a piece of jasper with iron ore brought by a pros- 

 pector from an outcrop near lake Temagami provides a reasonable source 

 of the jasper pebbles, and proves that the lower Huronian is represented, 

 to some extent at least, a few miles to the westward. 



Conclusions 



Granting that the ferriferous sandstones, cherts, and jaspers described 

 above belong to a definite horizon near the top of the lower Huronian 

 (or Algonkian), and that the conglomerates often found near by contain- 

 ing sandstone, chert, or jasper pebbles represent also a definite horizon 

 as basal conglomerates of the upper Huronian, some interesting conclu- 

 sions follow. 



In the first place, the gap between upper and lower Huronian is shown 

 to be a very profound one. Basal conglomerates, often thousands of 

 feet thick and found from point to point over a distance of more than 

 600 miles, indicate an erosive period of great extent" and significance. 

 In the next place, we have in these widespread rocks a means of corre- 

 lating the often widely separated and very different looking rocks 

 mapped as Huronian in Ontario. Doctor Lawson, in defining his Kee- 

 watin on the lake of the Woods and Rainy lake, came to the conclusion 

 that the highly metamorphosed schists and eruptives of that region 

 stood lower in the geological scale than the less altered quartzites, 

 etcetera, of the typical Huronian as described by Logan. If the ground 

 taken in this paper is correct, viz., that the Shoal Lake conglomerate is 

 at the base of the upper Huronian and the ferriferous sandstones found 

 at some points in the region belong to the lower Huronian, it is evident 

 that at least a part of the Keewatin is of Huronian age. Whether the 

 great beds of schist formed of pyroclastic materials and sheared eruptives 

 mapped by Doctor Lawson are older than the low r er Huronian, and so 

 should retain the name Keewatin as a separate formation, need not be 

 discussed here. 



The resemblance between the iron-bearing rocks shown to exist in 

 Ontario and the upper and lower iron-bearing series so carefully worked 

 out in Minnesota and Michigan suggests that they are of the same age, 

 and that the break between the upper and lower Huronian extends 

 along the south side of lake Superior as well as the north, though it is 

 too soon to state positively that this is the case. The detailed mapping 

 of the Vermilion series of Minnesota to the boundary of Ontario, which 

 Professor Van Hise informs me is about complete, will give an opportu- 

 nity to trace with more certainty the relations of these two great areas of 

 pre-Cambrian rocks. 



