366 M. D. Irving — Is there a Huronian Group ? 



rocks are found great developments of jaspery and cherty 

 ferruginous schists, whose identity as to nature and origin with 

 the ferruginous schists of the iron-bearing formations of the 

 south shore of Lake Superior, and of the Animike formation of 

 the north shore, seems complete. This identity, taken to- 

 gether with the close similarity of some of the fragmental rocks 

 of the Vermillion Lake band to the fragmental rocks of the 

 Animike and of the south shore iron-bearing formations, and 

 with the further similarity that obtains between the more dis- 

 tinctly crystalline schists of the Vermillion Lake band and 

 those of the older or gneissic formation of the south shore of 

 Lake Superior, suggests to us that we have here again to do 

 with a separation into an older and a newer schistose formation. 

 This suggestion is deepened into conviction when we further 

 consider the fact that the supposed older one of the two groups 

 of schists in the Vermillion Lake belt is intricately penetrated 

 by the granites of the great areas north and south of the belt, 

 while the same granites, where they come in contact with the 

 supposed newer schists, have yielded to them a profusion of 

 fragmental material, among which fragments are many derived 

 from the supposed older schists themselves. 



The appearance is, then, that the conditions obtaining in the 

 Vermillion Lake belt are analogous to those which present 

 themselves in the Menominee region, already briefly described, 

 with the difference that the folding and schistose structure due 

 to lateral pressure have been pushed to an extreme far greater 

 in the former region. 



VII. The several regions thus considered furnish us then 

 with a graded series as to the structural relations of the older 

 and newer rocks in each case. The Animike rocks lie upon the 

 older formation with only a slight inclination, and without folds. 

 The Penokee iron-hearing series, though still unfolded, lies with 

 a steep northern dip against a wall of the older granite-invaded 

 schists. Next in order comes the case of the unconformity on 

 the north shore of Lake Huron, where the typical Huronian 

 seines is gently bowed, but is without true schistose structure. 

 In the case of the unconformity of the Marquette region, the 

 upper group is crumpled between walls of the older schists, at 

 times even having the folds overturned, with frequent develop- 

 ments of slaty cleavage ; but still having the folds in the main 

 open, and presenting a true schistose structure only rarely. 

 In all of these cases — least distinctly of course in the last case — 

 the distinctness of the two formations concerned is' to be made 

 out in part from the visibly discordant positions of the rocks 

 of the two series. But when we proceed to the next case on 

 the list, that of the Menominee region, such discordances are no 



