THE NORTHEASTERN AREA. 457 



western end of the Republic trough in T. 47 N., R. 30 W., to the C Hue in 

 T. 45 N., R. 31 W., there are no exposures whatever of the Algonkian rocks 

 which underhe the Groveland formation. Somewhere in this distance of 

 about 11 miles the lower formations disappear, but whether by unconformity 

 or overlap is an unanswerable question; nor (for the same reason) can it 

 be definitely settled whether elsewhere farther to the south there is any 

 discordance. That there is general parallelism between the Groveland 

 formation and the lower rocks, and strict eonforiuity in some places, is true. 

 But this is not at all inconsistent with a period of erosion between them, if 

 that erosion antedated the later and more severe orogenic disturbance. 



In the Mesnard area the observed relations have been interpreted by 

 Van Hise to mean that the lower formations disappear by overlap. The 

 facts at present known on the Felch Mountain side are capable of the same 

 interpretation, but they are not sufficiently definite to exclude the possibility 

 of a period of erosion below the iron-bearing formation. 



With regard to the second consequence — the deposition in the sub- 

 merged areas of formations which would represent the erosion period in the 

 elevated area — the evidence at hand is decidedly against the existence of 

 such formations. 



The alternative hypothesis is that the lower quartzite, dolomite, and 

 slate formations of the Menominee area were not deposited over the 

 western Marquette area at all, but disappear toward the north and east by 

 overlap, and this hypothesis is much more likely to be the true one. We 

 can suppose, as I have already pointed out,^ that this part of the Upper 

 Peninsula was a slowly subsiding area, the central portion of which, now 

 occupied by the Marquette rocks, stood initially at a greater elevation 

 above the encroaching sea than the rest. While the quartzite-dolomite-slate 

 triad was going down in the Mesnard area on the east and the Menominee 

 area on the south and west, the central Marquette area still remained 

 above the sea. At last, when the Groveland formation began to be deposited, 

 the Marquette high land was finally submerged and covered, as the sea 

 marched over it, first, with a sheet of arkose made U2D of its own disinte- 

 grated ddbris, and, finally, with the same nonclastic sediments as chiefly 

 compose the Groveland and Negaunee formations. 



1 Relations of the Lower Menominee and Lower Marquette series in Michigan, by H. L. Smyth :: 

 Am. Jour. Soi., Vol. XLVII, 1894, p. 222. 



