L10 A. P. COL KM AN — UPPEB AND LOWER HURONIAN IN ONTARIO 



formation.* A mong other pebbles in the conglomerate he refers to some 

 of a chert-like stone. While studying this outcrop, which is well ex- 

 posed on the wave-beaten shore at the mouth of the Pore, and also on 

 islands to the south, the present writer found many pebbles, not only 

 of the cherty iron-bearing rocks, but also of the pulverulent sandstones. 

 Pebbles and boulders of all sizes, beautifully rounded and of a consider- 

 able variety of rocks — none, however, of typical Laurentian gneiss — are to 

 be seen here in a section dipping from 70 degrees to verticality, and with 

 a measured thickness of more than a third of a mile.t The conglomer- 

 ate has been traced by Professor Willmott and the writer about 17 miles 

 from east to west and probably extended still farther, since small out- 

 crops of conglomerate are found to the east. Belts of conglomerate are 

 seen also within 2 or 3 miles of other parts of the sandstone range, but no 

 search has yet been made for pebbles of sandstone or jasper. It is evi- 

 dent that the Dore conglomerate marks a very important break in the 

 Huronian of the region, and it is probable that the other conglomerates 

 referred to are to be looked on as of the same age. The lack of Lauren- 

 tian pebbles shows that they are not basal conglomerates of the Huronian 

 resting on a Laurentian floor, and the chert and sandstone pebbles prove 

 that they are more recent than the iron-bearing series. 



Conglomerates near Rainy Lake 



A very extensive series of schist conglomerates has been mapped by 

 Lawson on Shoal lake east of Rainy lake, and was thought by him to be 

 a basal conglomerate of the Keewatin above the Couchiching.| The 

 same region has been examined by Winch ell and Grant, who report that 

 black and red jaspers occur in it as pebbles,§ and by the present writer, 

 who found numerous pebbles of pulverulent sandstone, as well as of 

 cherty materials, along with the more common felsite and porphyry 

 pebbles. 1 1 This conglomerate has been traced for about 15 miles from 

 southwest to northeast, and probably has a thickness little short of a 

 mile. That it represents a very profound break in the Keewatin series 

 is shown by the fact that among its boulders are some of anorthosite 

 evidently derived from an adjoining mass of that rock. The anorthosite 

 itself is proved to have erupted through rocks apparently belonging to 

 the lower Keewatin, since it carried off in its eruption fragments of 

 chloritic and sericitic schist exactly like certain Keewatin rocks of the 



*'Geol. Can., 186:5, p. 54. 



fOnt. Bur. Mines, vol. viii, second part, 1899, pp. 165-167. 



tGeol. Sur. Can., 1887-88, p. 82 F. 



g Geol. Sur. Minn., 23d Ann. Rep., 1S94, p. 66. 



|| Ont. Bur. Mines, 1895, p. 97. 



