GEOLOGICAL EXPLOKATIONS AXD LITEKATUKE. 71 



Presque Lsle river, in SE. ^ of Sec. 17, the bed of wliieli stream is carved there diiigo- 

 iially aeross the stratificatioii iiitu the lilack uraphitie slates, which form here also a 

 very thick succession of beds. 



A mile farther west, in the SE. ^ of Sec. 18, T. 47, K. 43, 1 met for the first time with 

 outcrops of dark purple-colored banded quartzite beds, formed of alternating seams 

 richly impregnated with sj)ecular ore grains, and others of a more purely quartzose 

 composition. The rock belt to which these strata belong is csi)OSpd in the bed of a 

 small creek, but the exposures are too limited to otter a cross section giving informa- 

 tion of the thickness of this belt and of the rock adjoining it; but as the trend and 

 dip of the beds are in conformity with the graphitic slates and the galeua-bearing 

 quartzites, it is probable that they belong approximately to the same geological hori- 

 zon. West of this creek the trail follows the south line of Section 18, and then of 13 

 and 14 in the adjoiuiug township as far as the Little Presque Isle river. 



The quotations tlm.s given from Dr. Roniinger under the head of the 

 Iron Ore group, refer essentially to those slaty quartzitie and partly ferru- 

 ginous rocks which lie to the east of the Presque Isle river and north of the 

 great area of brecciated greenstone-schist subsequently described. (See 

 Plates II and x.) On account of the difficulties in i-eading the structural 

 relations of this belt the quotations are made quite full. The remainder of 

 Dr. Rominger's remarks under this heading consist only of unim})ortant 

 descriptive details with regard to the exposures of ferruginous rocks 

 between the Little Presque Isle and Montreal rivers. 



In addition to the foregoing, the following general remarks are worthy 

 of quotation here, since they define Dr. Rominger's position as to the rela- 

 tive ages of the granitic rocks and the iron-bearing slates which rest upon 

 them. As already noted. Dr. Roniinger had previousl)- })ublished the o})in- 

 ion (Geological Survey of Michigan, vol. iv, p. 6) that the granitic rocks of 

 the Upper Peninsula of Michigan are all newer than the various schistose 

 and slaty rocks of the region into which he conceived them to have 

 erupted — as did also Foster, Whitney, and Wadsworth before him — and to 

 have produced the crumplings and alterations these schists now present 

 us with. Subsequently to the publication (if these \'iews certain consider- 

 ations were urged on Dr. Roniinger by the present writer, going to show 

 that these granitic and gneissic rocks are really older than a large portion 

 of the schistose and slat)- rocks; for, while tkey have invaded a portion of 



