G?mERAL (iEOLOGV OF THE DI.STRICT. 457 



stone or quartzite. That there is a great time gajj Ix'tweeii the Southern 

 Complex and the Penokee series lias just been shown. That there is also 

 a time interval, although not so vast a one, between the iron-bearing and 

 the overlying KeweenaAV series, is equally clear. In any single section this 

 discordance is not plain, for the Keweenaw rocks north of the Penokee 

 series, like the latter, have as a whole a northern di]) at a high angle.' The 

 eruptive character of the basement member of the Keweenaw series for 

 most of the distance, and its northern inclinntioii, make it more difficult tf) 

 prove an unconformitv between the two than between the Penokee series 

 and the Southern Complex. The proof here rests entirely u}ioii broad field 

 relations; unless the conglomerate, placed ]irovisionalU' at the top of tlie 

 Upper slate (pp. 305, 32G), belongs with the Keweenawan. This conglom- 

 erate lies but 200 stejis south of the Keweenawan greenstone. It is sep- 

 arated from the typical biotitic slate (p. 326) of the Upper slate member by 

 an unexposed interval of 280 steps. The pebbles, ranging up to eight or 

 ten inches in diameter, are mainly of white quartz, but tlint and black 

 honistone are also abundant. The most [)robable source of the last two 

 are the Chertv Limestone and Iron-bearino- members of the Penokee 

 series. While it can not be asserted whether this conglomerate belongs to 

 the Upper slate, or at the base of the Keweenawiin, the latter alternative is 

 the more jirobable, and if this be true, the rocrk may he considered a basal 

 conglomerate. 



Beginning at the west end of the Penokee succession, and following 

 the contact of the two series of rocks to the eastward, it becomes evident 

 that there is a considerable break between them. Near the northeast corner 

 of Sec. 20, T. 43 N., R. 7 W., Wisconsin, characteristic eruptives of the 

 Keweenaw series, as found l)^' ]\Ir. Charles E. Wright," are upon tlie north 

 side of Numakagon river, and a g-neissoid granite of the underlying complex 

 upon its south bank. It is not certain that rocks belonging to the Penokee 

 series are not between, but there is no proof of this or of their existence to 

 the westward for a long way ; so this point may be taken as the western- 



' Cojiper-beariug Rot-ks of Lake Superior, pp. 225-234, R. D. Irving, T'. S. (Jeol. Survey, Mono- 

 graph, vol. V. 



'Geol. of Wis., vol. ill, p. 300. 



