THE UPPER SLATE MEMBER. 301 



the same process of" tilting-, and which has resuUed, in connection with 

 erosion, in givinjr the series its present surface distribution. 



Topographical features. — The topography of the Penokee district (Pis. 

 VII, IX, and xi) shows in a general way the boundaries of" the Upper slate 

 member. The ridg-e known as the Penokee range has been described in 

 detail, pp. 145-146. It is always found witliin the Quartz-slate or Iron- 

 bearing members, or in the granite just to the south. North of the iron 

 formation the ground slopes rapidl}' in most cases to a nearly level plain, 

 which ordinarily has a gentle slope northward, as is shown by the direction 

 of the flow of the streams (PI. ii). A considerable portidu of the ground 

 is of a swampy nature, and the part not a swamj) is largely low, rich, 

 heavily timbered and thick with underVjrusli. The northern boundary of 

 the Upper slate is for much of the distance defined b}' the trap range, 

 which constitutes the base of the Keweenaw series. In traveling from the 

 iron range north across the slate belt to determine its mirtheni limit, the 

 approach to this line is indicated by a rise in the ground. Ascending the 

 swell for a short distance, oue is pretty sure to find the eruptives of the 

 Keweenaw series, and oftentimes in the form of a series of bold Ijluffs, 

 which are a prominent topographic feature of the region. In general, then, 

 the Upper slate mendjer lies in a valley, bounded by the Penokee range on 

 the south and the trap range on the north. At many points on both of 

 these ranges the valley may be overlooked. The tree tops are seen stretch- 

 ing as an almost level mass of forest for miles both east and west. This 

 forest is now rapidly disappearing under the necessities of the neighboring 

 mines. 



Within the belt the exposures are usually h)w and sniMJl. This i-esults 

 from the soft chanicter of the slate. It is to be presumed thiit t lie judg- 

 ment made up from the known exposures conveys a somewhat eiToiieous 

 impi-ession with reference to the character of the meml)er as a whole ; that 

 is, the rocks which have a certain amount of the more resistant massive 

 graywacke or quailzite are more a[)t to be exposed than the softer slates. 

 In the vicinity and a short distance west of Bad river the ex[)osures are 

 quite numerous; also a little way west of this locality, east of English lake, 

 there are again frequent exposures. This unusual nund)erls here probably 



