454 THE PENOKKE IHON-P.EAKIXG SERIES. 



member. Wlieii the basement rocks are green schists their fohatioii had 

 been devek:)ped and they had been tnincated; when they are |j-ranite, if 

 formed at depth, it had readied the surface by erosion. Fourth, the fact 

 that the horizon at which tlie underlying compk^x is in contact witli tlie 

 Penokee series proper does not vary more than 300 or 400 feet at the out- 

 side is the clearest sort of evidence tliat the underlving rocks had nearly 

 reached a "base level" before .the beginning of tlie deposition of the Peno- 

 kee series.' 



The iinconformif}! between tlie Chert i/ limestone and the renokee series 

 proper. — In the description of the Quartz-slate ((Jhapter iv) it was seen that 

 at a number of places this member contains in its basal portions abundant 

 debris derived from the chert of the Clierty limestone, becoming in several 

 places a genuine chert-cong'lomerate. This derivation is indicated by the 

 lithological likeness of the pebbles of the conglomerate and the chert (»f 

 the limestone, as well as by the fact that these conglomerates are usually 

 found near, some of the exposin-es of the limestone. At Penokee gap the 

 Quartz-slate rests directly upon the (Jhertv limestone, being here a recom- 

 posed (|uartz-rock nearlv all of the debris of which comes from the innne- 

 diately subjacent member." 



Beginning at the west and passing east these reccMiiposed rocks or 

 conglomerates have been found at Penokee ga]), mount Whittlesey, Potiito 

 river, near the Palms mine, and east of Sunday lake at several })oints in 

 Sees. 10, 14, and If), T. 47 N., R. 45 W., Michigan. In all tliese cases the 

 chert pebbles derived from the Clierty limestone are well rounded and in 

 exactly the same condition as the chert now is in the limestone. Tliese 

 pebbles apjiear to be clear evidence that the limestoiK* had become clierty 

 before the deposition of the lowest member of the Penokee series proper. 



' TliB time gaji implied Uy such an uncoutbrmity as the above is fully discussed by Prof. Irviug, 

 U. S. Geol. Survey, 7th Anuual Report, pp. 390-143. Suffice it here to say that it is clearly showu 

 thatan uuccmfonnity of this sort, indicates "a lapse of time long euough Jo cover (1) the folding of 

 the lower series, (2) its elevation into a land surface, (3) a long continued di'nndation," and (4) its 

 depression under the sea. "In other words, it indicates an interval of more or less e.\teuiled 

 orographic movement, with its accompanying • • « denudation." In this case it is plain that 

 the orogra]diii' movement is of a most extended character. 



^(ieology of tlie Eastern Lake Superior District, K. I). Irving. Tlie reeomposed rock is Irviug's 

 IIB, Geol. Wis., vol. iii. iip. l(l!t, llli. 



