262 JR. D. Irving — Is there a Hxironian Group f 



and south section midway in Gunflint Lake is given herewith 

 to illustrate these relations. So far as it is developed along 

 the national boundary line the lowest layers of the Animikl 

 series in sight are those on Gunflint Lake. The highest layers 

 are those in the vicinity of Grand Portage Bay. the whole suc- 

 cession between these points being some thousands of feet in 

 thickness. The iron-bearing horizon at the base of this suc- 

 cession is lithologically identical with that of the Penokee 

 series of northern Wisconsin and Michigan, while the black 

 slates, greywackes, etc., which succeed the iron-bearing horizon 

 are in turn the counterparts of those which form the middle 

 and upper portions of the Penokee series. The interstratified 

 gabbros of the Animike are wanting, however, or are relatively 

 rare in the Penokee region. 



In attempting to trace the Animike rocks from this area 

 farther west than southwest we find ourselves constantly 

 balked by the overlapping layers of the Keweenaw series. 

 This overlap will be best appreciated on an inspection of the 

 accompanying map, upon which it is shown that the basal 

 olivine gabbros of the Keweenaw series entirely cut out the 

 Animike in its surface distribution, coming, a few miles to the 

 northward of Gunflint Lake, directly into contact with the 

 older schists. Continuing southwest nothing farther is seen 

 of the flat-lying Animike beds for over fifty miles, but in 

 the vicinity of the south side of Birch Lake they emerge from 

 beneath the overlapping gabbro. From here the lower mem- 

 bers of the series, with the usual flat southeasterly dip, and 

 with the lithological characters well-preserved, may be traced 

 along the south side of the Mesabi granite range as far as the 

 Embarrass Lakes, a distance of some twenty-five miles ; in 

 which distance they are plainly in unconformable abutment 

 upon the granite to the north. After this they are concealed 

 entirely, so far as present knowledge is concerned, by the 

 immensely heavy drift-covering of the region, until the vicinity 

 of Pokegama Falls on the Mississippi River is reached, some 

 sixty miles farther to the southwest. Here the basal layer of 

 the Animike' is a reddish quartzite followed by, and associated 

 with, layers of cherty iron ores like the remaining ones of the 

 Animike series. These layers dip at the usual flat angle to 

 the southeastward and rest unconformably upon gneiss and 

 granite, which are plainly the direct continuation of those of 

 the Mesabi range. 



Southward and eastward of the line from the Mesabi range 

 to Pokegama Falls the rocks are mainly concealed by swamp 

 or heavy drift covering, but a great display of the upper por- 

 tions of the Animike series is seen again along the St. Louis 

 Eiver from Knife Falls to Thomson, where they are cleaved 



