536 THE JOURNAL OF GEOLOGY. 



erate is a quartzite which includes the Mt. Mesnard and Teal Lake quartzites. 

 In Sec. 20, T. 47 N., R. 26 W., and Sees. 8 and 19, T. 49 N., R. 28 W., near 

 Silver Lake and in other places, sediments of the Holyoke formation have 

 sifted down into the fissures and joints of the preexisting rooks, when they 

 have a dyke-like character. For such formations the term "clasolite" is 

 proposed. The dolomite of Mt. Mesnard and thence to Goose Lake, while 

 lithologically, like that placed in the Republic formation, is doubtfully referred 

 to the Holyoke. Argillite, graywacke and mica-schist occur extensively 

 in the Holyoke, constituting the upper horizon. It is doubtful whether any 

 granite or felsite of Holyoke age exists in the Marquette district. 



Diabase, diorite, porodite, and peridotite occur abundantly, belonging 

 both to the Republic and Holyoke formations. According to Mr. Seaman, 

 diabase dykes of the Gogebic area are probably the same as those that cut 

 the overlying sandstones of the Keweenawan, from which it is concluded that 

 the Keweenawan lava flows are the effusive equivalents of the Holyoke dia- 

 base dykes. 



The soft hematites of the region are produced by secondary enrichment 

 at places where the water could best act, being at points of fracturing or in 

 basins. The silica of the lean material has been leached out, and in its 

 place iron oxide substituted. Gold and silver veins are discussed, and a 

 classification of ore deposits given. 



The Eastern or Potsdam sandstone rests unconformably on the Azoic. 

 This includes the unaltered horizontal sandstone, which is free from dykes of 

 eruptive material, and the Keweenawan, which consists of lava flows alter- 

 nating with sandstones and conglomerates, largely derived from the former. 

 Above, and conformably with the Eastern sandstone, near L'Anse, is lime- 

 stone of Silurian age, as shown by its fossil contents. On Keweenaw Point 

 the Eastern sandstone dips toward, and passes under, the interstratified sand- 

 stones and lavas of the Keweenawan. At or near the contact is a fault. 

 However, at Douglas, Houghton and Hungarian rivers, it is thought not to be 

 at the contact, and consequently that the Eastern sandstone underlies the 

 Keweenawan lava, but the Eastern sandstone may contain two or more sand- 

 stones of different ages, which may perhaps be considered as the most proba- 

 ble explanation of all the evidence. In Sec. 13, T. 46 N., R. 41 W., on the 

 South Trap range, a nearly horizontal, soft, friable micaceous sandstone is 

 found near the interbedded Keweenawan melaphyr and indurated sandstone. 

 This soft sandstone contains numerous spherical spots very common in the 

 Eastern sandstone, but not found in the Keweenawan. In the soft sandstone 

 are found pebbles and large angular fragments of indurated sandstone, which 

 Mr. Seaman thinks could only have been derived from the adjacent indurated 

 sandstone. The rocks of the Trap range here exposed are believed by Mr. 

 Seaman to hold a position near the top of the Keweenawan series, and he 



