EELATIONS OF UPPER HURON IAN SERIES. 163 



tuff deposited upon the land, or is water-deposited volcanic material, and 

 thus possibly a basal coug-lomerate of the Upper Huronian. 



In sec. 34, T. 46 N., R. 33 W., the Lower Huronian and Upper Huronian 

 are found in very close proximity. Here the Upper Huronian is a ferruginous 

 graywacke and is separated by only about 10 yards from the schistose vol- 

 canics. In this case careful search failed to reveal the intermediate rock. 

 In only one case in addition to the Amasa instance has a distinct conglom- 

 erate been found which can be considered as a possible basal conglomerate- 

 This is in sec. 9, T. 42 N., R. 31 W., along the Michigamme River. Here 

 there is a thick mass of conglomerate overlain by southward-dipping schists 

 The conglomerate contains pebbles of extremely altered basic amygdaloidal 

 rocks and of acid rocks which rest in a matrix of chlorite-schist. This 

 detrital rock is such as might be derived from the Hemlock volcanics, but 

 between it and these volcanics is found a mass of ferruginous muscovitic and 

 chloritic schists at the Glidden exploration (sec. 32, T. 45 N., R. 31 W.), which 

 are very similar to those occurring immediatel)^ south of the conglomerate, 

 and like them have apparently a southern dip. The true relations between 

 this conglomerate and the schists at the Glidden workings are not certain. 

 The conglomerate' may be below them. In that case the Glidden schists 

 would correspond to those south of the conglomerate, the beds having 

 received their present distribution from the close folding to which they have 

 been subjected. 



If such be the case, the schists at the Glidden are the northern limb of 

 a syncline, and the coiiglomerate and the overlying schists, with an average 

 dip of 70° S., represent the southern limb of a steep anticline, whose crest 

 and northern limb have been cut off and covered up. The considerable 

 width of the conglomerate exposed may be partly due to the fact that it 

 has been doubled upon itself. 



That the folding in this part of the district was probably fully sufHcient 

 to produce such structural relations and also the petrographical changes 

 of the conglomerate matrix to a chloritic schistose mass is shown by the 

 changes which the sedimentaries south of them in this pai't of the district 

 have undergone. If this interpretation is correct, the space between the 

 schists at the Glidden exploration and the Hemlock volcanics should be 

 occupied by the equivalents of the conglomerate. Section K-L, PI. VI, 

 embodies this idea of the structure. 



