180 BULLETIN lO:), U2?ITED STATES NATIONAL MUSEUM. 



about equal in amount to the conglomerates. The materials are simi- 

 lar to the conglomerates ; while those of the true sandrock lying above, 

 ore chiefl.y quartzose. The conglomerate and the mixed conglomer- 

 ates and sandstones are composed essentially of rounded frag- 

 nients of greenstone, and "the whole may perhaps be regarded as 

 a trap tuff" (p. 37). While the coarser conglomerate scarcely 

 shows lines of stratification, these are very distinct in the sandstones. 

 That the latter were deposited in shoal water is further evinced by 

 the perfectly defined ripple marks. • " Dikes of greenstone occasion- 

 ally appear in the mixed rock, but they almost invariably occupy 

 places between the strata." There are also many cross veins, made 

 up usually of calcareous spar or a sabgranular limestone, and more 

 rarely of some variety of quartz and imperfect amygdaloidal trap. 



6. Loioer or red sandstone and shales. — These cover more space 

 than any other formation. They rest upon the primary or meta- 

 morphic rocks, immediately west from Chocolate River, upon the 

 conglomerate and mixed rocks from near Eagle River to the west end 

 of Lake Superior. The situation is similar on He Royale and the 

 north shore. These rocks are thickest Avestward. The predominat- 

 ing rock along the immediate shore of the lake is the red sandstone. 

 The dip on both shores is toward the lake. It flanks all the hills and 

 ranges of primary, metamorphic, and trap rocks. In the sandrock 

 magnetic iron sand is a frequent constituent, sometimes forming 

 strata of several inches. The rock material is cemented by calcareous 

 matter highly colored by peroxide of iron. On the southeast side of 

 Keweenaw Point the exceptional argillaceous strata, found also at 

 several points in the interior, are regarded as constituting a member 

 of the sandstone series. It sometimes appears as a slate, but the 

 usual condition is that of an indurated clay. It is extremely fine; 

 is easily cut with a knife, and the Indians have long been accustomed 

 to work it into pipes. 



The rocks of the red sandstone formation are abundantly and 

 beautifully characterized by ripple marks. Of fossils, nothing but 

 some fucoids has been discovered, " of which there are three species 

 pretty well defined."' 



But few dikes intersect the sandstone, except wliere the intervening 

 conglomerate and mixed rocks are wanting. Here the sandstone as- 

 sumes a deep brown color, " and the material of which the sand is 

 composed gradually changes from that before described to green- 

 stone " (p. 40). 



The greatest thickness at the west was estimated at 6,500 feet. It 

 is regularly alternated eastward. The average rate of alternation is 



* These have been descrilied by the writer (i. e., A. WInchell] as two species. Hee 

 Amer. Jour. Scl., ser. 2, vol. 37, pp. 226-233, 1864. 



