GEOLOGICAL EXPLORATIONS AND LITERATURE. 35 



Col. Whittlesey's luaps aud seetioiis, given in Owen's leixtrt, 1853, represent a 

 belt of granite, syenite, and iiornblende rocks as dividing the Penokie series (Huron- 

 lau) from the overlying Oopiier-beariug amygdaloidal traps aud sandstones, which lie 

 to the north and nearer the lake. 



1 observed tliese rocks at several points in 1871, and noted their general lithe, 

 logical resemblance to the Laiirentian, as well as the almost iusuruiountable structural 

 difficulties in assigning tt) them that age, and recorded in my notes the probability of 

 tlieii' being Upper Ilurouian. Rowland Irving mentions these rocks as being coarsely 

 crystalline aggregates "chiefly of labradorite and ortlioclase feldsjiar, hornblende, 

 and some variety of iiyroxene," with occasional evidences of bedding, which points 

 toward their entire conformability with the underlying Huroniau. He regards them 

 as of the period of the Gopper-bearing series, constituting its lowest and oldest 

 portion. 



Having been, so far as I know, but little studied, it is perhaps impossible at this 

 time to determine their age; but what is known can here be briefly surveyed, and an 

 inference drawn, whicli will not be without value in directing further investigations. 



1. The general lithologieal similarity of this granitoid belt to the Laurentian 

 has been remarked. It has (piite as nmch similarity, if not more, to several members 

 of the Hurouian, and is, I believe, not identical with any rock known to belong to the 

 Copper series. 



3. Its geographical extension is peculiar in this, it wedges out rapidly to the 

 east from the vicinity of Penokie gap, entirely disappearing at the Montreal river, 

 which divides Michigan and Wisconsin. Prof. Pumpelly and myself traced the 

 boundary l)etween the Copper and Huronian rocks 30 miles fiirther eastward beyond 

 lake Gogebic, without again observing it, which we should certainly have done if it 

 had existed there, for we often found the two series very near together, although the 

 actual contact was not seen. 



3. Not only does this granitoid formation thin out and disappear in its eastward 

 prolongation, but the same is true of the whole Hurouian series, the belt of which 

 becomes narrow as followed east, and finally disappears in the neighborhood of 

 Gogebic, where the Laurentian is seen very near the Copper series. 



4. The fact that the granite mass does not cross either tlie Copper or Hurouian 

 series, or, so far as observed, give off dikes in either, renders it improbable that it came 

 into its iireseut position as an eruptive mass subsequent to the formation of both 

 series of rocks. 



5. The various ores of iron, which are so generally and abundantly diffused in 

 the Lower and Middle Huronian, are entirely absent so far as observed from the 

 upiier three or four members as developed in the Marquette and Menominee regions, 

 and also in the Penokie series if the following hypothesis is true; but they occur in 

 all forms, although it is believed not abundantly in the uppermost exposed member 



