174 



THE CAMBRIAN. 



[Bull. 81. 



nous and argillaceous sandstones, shales, and conglomerates at the base, 

 assigning it a thickness of 5,000 feet. Above this occur coarse grits and 

 sandstones of the Chippewa, Black and Wisconsin Rivers. 1 The placing 

 of the lower sandstone of Lake Superior in this position is theoretical. 

 Above the coarse sandstone the formation is divided into six trilobite 

 beds, as follows : 2 



Table of the elementary stratification of the lowest Protozoic sandstones, — 



Formation 1. 



Sixth Trilobite bed... < 



/•< 



e. 



d.l 



'Quartzose, light-colored sandstones of various 

 degrees of induration, with intercalations of 

 beds of maguesian limestone, with glisten- 

 ing crystalline facets, and calcareo-siliceous 

 oolite,produced by rounded grains of quartz, 

 encased in calcareous cement, containing 

 Euomphalas and imperfect Trilobites. Lo- 

 cally with a band of green earth 



Mammillary and botryoidal layer of white 

 sandstone ; sometimes banded with yel- 

 low 5 to 6 inches. 



f Thick beds of soft, yellowish and brown sand- 

 stone, sometimes with botryoidal, hard, pro- 



^ jecting concretions passing downward into 



fine-grained soft sandstones approaching 



t tripoli 



f Ash-colored and yellowish argillo-calcareous 



Fifth Trilobite bed. .J *?? magnesio-calcareous beds, containing 



] Dikelocephalus mmnesotensis. 



I St ill water Trilobite bed 



Green, red, and yellowish sandstones with thin, 



schistose, dolomitic intercalations 



Upper, brown dolomitic layers containing 

 Orthis, Lingulas, and columns of Crinoidea 



as at La Grange Mountain 



( Alternations of yellow, laminated sandstones, 



Fourth Trilobite bed. . < with green particles disseminated 



( Marine Mill Trilobite grit 



Fucoidal layers, and thin-bedded green and 

 yellow sandstones, at their base often a 

 band of about 6 inches of green earth used 



by the Indians as a pigment 



Green and red sandstones, charged with sili- 

 cate of iron 



Loose, green sand, and soft green sand- 

 stone 



( Micaceous sandstone, containing Dikelo- 

 I cephalus meniskaensis, D. granulosa, etc .... 



Third Trilobite bed I Alternations of green and ferruginous sand- 



stones ...................................a 



Micaceous sandstones containing D. menis- 



kaensis, etc 



Thin layers of green sand, alternating with 

 green earth, impregnated with silicate of 



iron '. 



Lower, brown siliceo-calcareous and dolo- 

 mitic bands of Mountain Island, and else- 

 where 



Soft, thin-bedded sandstones, with scales of 



mica disseminated 



Coarse lingula grit, green, yellow, sometimes 

 almost white 



Feet 



50 to 85 



40 to 50 



8 to 10 

 40 



30 to 40 

 5 



15 

 3 



20 

 2 



30 to 40 



4 



10 to 15 

 100 to 130 



1 Op. cit., p. 53. 



» Op. cit., pp. 52, 53. 



