154 LOWER PENINSULA. 



On the western slope of the ridge we find the trap rock overlaid 

 by a heavy series of sand rock, conglomerate, and slate deposits, 

 resting conformably on the trap, and participating in its upheavals. 

 The age of these beds is intermediate between the trap and the 

 horizontal sandstone deposits ; but between all three of the indicated 

 groups so great lithological affinities exist, that it is most natural to 

 consider them as the consecutive products of one and the same 

 epoch, in the commencement of which the just-formed strata were 

 displaced by volcanic action, which subsided toward the end and 

 left the last deposits undisturbed. 



The trappean series is not clearly definable from the conformably 

 incumbent higher beds which form the western slope of the range. 

 The crystalline or amygdaloid trap seams are underlaid by conglo- 

 merates and „by ripple-marked brown sandstones which are abso- 

 lutely undistinguishable by lithological characters from similar rock 

 beds found deposited above the trap, and the only way in which 

 the two horizons can be distinguished is by observation of their 

 relative positions to the underlying or incumbent strata of a certain 

 Avell-marked lithological character. 



The absence of all trappean rocks distinguishes the upper divi- 

 sion from the lower, in which a constant alternation of trap with 

 the sedimentary beds is observed. 



The lately discovered silver-bearing rocks are sedimentary strata 

 inclosed within the more recent non-trappiferous division, which con- 

 formably leans with its uplifted beds against the higher trappean hill 

 range, forming a sloping belt of lower hills between the higher range 

 and the lake. 



In the north part of Kewenaw peninsula, this shore belt is form- 

 ed by sandstones very little affected by the upheavals, and litho- 

 logically very similar to the horizontal sand-rock beds on the east 

 side ; they seem to be somewhat younger than those forming the 

 belt at the foot of the Ontonagon range, and are, as far as known, 

 not metalliferous. 



In the interval between the mouth of Ontonagon River and the 

 Porcupine Mountain spur, this rock series under consideration is of 

 somewhat different lithological character ; its beds are considerably 

 dislocated by upheavals, and certain seams of the formation are rich 

 in metallic silver, while others are so in metallic copper. 



The thickness of this rock series in Ontonagon district is very 



