GEOLOGICAL EXPLORATIONS AXD LITEKATURE. 49 



chiefly {jabbnis, arc of an igueoiis origin, and havt; certainly, in some places, and 

 quitr possibly, also, in others not yet recognized, i)cnetrated the Huronian, producing 

 peculiar irrciiularities in the line of junction. 



Tlie main topngraiihical features of the JIuronian belt have already been given 

 in another connection. It is only necessary to notice here somewhat more definitely 

 the rehition existing between the geological structure of the series and the topography 

 of the strip of country uiulerlaid by it. The Iluronian series includes a succession 

 of beds, always markedly schistose and at times highly slaty, which are, for the most 

 part, inclined at a high angle to the northward. At the base or southern side of the 

 belt are narrow layers of crystalline limestone and (jnartzite, succeeded by a broad 

 band of siliceous slate, some -iOO feet in width, above which th^i'e is again a nuich 

 broader baud, generally as much as 800 feet wide, of magnetic and specular schists. 

 Above these again is a series of alternating layers of mica slates, diorites, quartz 

 slates, and quartzites — the latter comparatively inconspicuous — which reaches a thick- 

 ness of several thousand feet. A close connection may be traced between the nature 

 of these beds and the features of the surface. 



The existence of the Peiujkee range, which marks the lower side of the Huronian 

 belt for the greater part of its extent, and which has already been described in some 

 detail, is determined by the broad bed of magnetitic quartzites and siliceous, mag- 

 netic, and specular schists above referred to. These, by virtue of the superior hard- 

 ness and power of resisting chemical action conferred on them by their siliceous 

 ingredient, have remained standing, while the softer beds to the north have been 

 worn, for the most part, into deep valleys, in which streams run parallel to the trend 

 of the Penokee range, being impelled to their courses by the strike of the under- 

 lying rocks. In jjlaces the more massive diorites and quartzites of the northern 

 portion of the scries rise ft-om the valley in abrupt ledges, but they never constitute 

 a continuous ridge like the Penokee range, on account of their smaller breadth and 

 inferior resisting power. On the northern side of this valley the Huronian beds often 

 extend well up the river on to the Copper range, being protected here by the massive 

 rocks of the Keweenaw series, which bound them on the north. The south slope of 

 the Penokee range, again, is made up of the siliceous schist whicii uiulerlies the 

 harder rocks that form the body of the range, and, being itself generally a quite soft 

 and easily eroded material, the southern slope is often precipitous, or at least very 

 bold. This is especially true of the middle portions of the range, from a few miles 

 west of Bad river nearly to Tyler's fork. Further east this layer becomes more 

 quartzitic and harder and forms itself the body of the ridge, the overlying beds at 

 the same time losing their comparatively great resisting power by a change in com- 

 position. In some places in the eastern extension of the Huronian belt both the 

 siliceous schist and the overlying beds are softer than the Laurentiau below, and the 

 crest of the ridge is made up of rocks of the latter series, 

 nov XIX i 



