116 C. P. Williams and J. F. Blandy, 



the question of the identity of the rocks of the eastern portion 

 of the Isle Eoyale series with some of those known to occur in 

 the Salphuret range, since instances of the thining out of belts 

 of trap have been observed and well proven by explorations at 

 Portage Lake, as well as elsewhere. The Isle Eoyale series of 

 rocks widens out northeasterly from Portage Lake towards Point 

 Keweenaw. The Pewabic series widens out towards the north- 

 east, and thins out southwesterly at the rate of over sixty feet 

 to the mile; and the Hancock zone also becomes wider towards 

 Point Keweenaw, but the rate of increase is much less than in 

 the case of the Pewabic rocks— amounting to but about filteea 

 feet in the mile. 



In the Keweenaw Point District it has been shown by recent 

 researches that the series of rocks in which the Cliff vein has 

 been found most highly productive, recedes from the greenstone 

 in its easterly prolongation, other belts of compact and amygda- 

 loid traps being introduced between the crystalline belt and that 

 series, the rate of increase being in all probability much greater 

 than anything noticed above. 



Towards the Ontonagon District the trap range again widens 

 out, and at its southern boundary we find a series of ridges made 

 up of rocks analogous in structure and identical in mineralogical 

 composition with the belts found making up the Isle Rovale 

 zone. The mineral accumulations here are also in the form ot 

 segregated deposits, called "epidote lodes"— that mineral enter- 

 ing largely into their composition. The so-called veinstone isot 

 such appearance as to be readily confounded, even by the expe- 

 rienced eye, with matter from the Isle Eoyale lode at Portage 

 Lake. 



Traces of the sulphids of copper have been found in this re- 

 gion also, on the southern limit of the United States location,!^ 

 well as elsewhere. The course of these rocks is through the 

 Evergreen Bluff, Peninsula, Forest, United States and Ohio Trap 

 Eock locations. 



Thus, from the end of Point Keweenaw to a very considera- 

 ble distance beyond Portage Lake the rocks which we have cla*- 

 Bified as belonging to the Isle Eoyale series, appear to exist » 

 or near the base of the Trap Eange of Lake Superior, but in tb« 

 western prolongation of the Range, towards the Wisconsin bound- 

 ary line, another series becomes developed, as is shown by tn- 

 works at the Korwich mine, but little is known of the relation 

 or composition of these rocks. However, a bed of fissile coi*-'' 

 rite rock which we have reason to suppose is identical with tfl<^ 

 rock we have described at the base of the range at Portag^^ 

 Lake, has been opened at the southern limit of this series oi 

 rocks, and is shown at the mouth of the adit of the Windsor 



