THE IKON-BEARING MEMBER. 233 



From the section on the Tilden mine property. 



41. ITematitif flint or chert, from a middle horizon. Specimen 7571 (slide 1993); 

 from 1500 N., 1215 W., Sec. 15, T. 47 N., K. 4<; W., Michigan. 



The thin section is a chert containinj;- nuich finely divided hematite^ 



42. Ileinatitic flint or cliert, from a middle horizon. Specimen 7565 (slide 20G4); 

 from 1450 N., 1185 W., Sec. 15, T. 47 N., R. 46 W., Michigan. 



The section is a hematitie flint analogous to that of 41. The hematite in tlie 

 larger part of the section is, however, more uniformly contained and in more minute 

 particles. It is arranged so as to show faint hut perfect concretions. In parts of the 

 section are couceutrated large areas of hematite. 



From the .lection on the Palms property, 



43. Cherty and altered iron carbonate, from a middle horizon. Specimen 7573 

 (slide 1996); from 1600 N., 1955 W., Sec. 14, T. 47 N., R. 46 W., Michigan. 



About half the area of the thin section is a light gray and tlie other half a red- 

 dish brown. The light colored portion is composed of nnifonnly mingled minutely 

 crystalline quartz and gray siderite. The siderite occurs within the siliceous ground- 

 mass both in detached individuals and in complex areas, the single individuals 

 showing usually very distinctly the rhombic outlines. The bi'own portion of the slide 

 is like the other pcu'tion so far as the siliceous groundmass is concerned, but here the 

 brown and red oxides of iron take the place of the siderite of the lighter colored part 

 of the slide. Since these iron oxides show often the same rhombic outlines as seen in 

 the siderite; since they occupy precisely the same relation to the chert; since there is 

 a grailation and not a shari* definition between the two portions of the section; and, 

 finally, since the single individuals of siderite may be seen partly changed to iion 

 oxide, it is evident that the latter mineral is a secondary product of the former. 



From the section on Black river. 



44. Jasper and ferruginous chert, from very near the base of the Iron-bearing 

 member. Specimens 9508 (slide 29S3), from 1665 N., 1915 W.; 0509 (slide .•!137), from 

 1600 N., 1900 \V.; 9510 (slide 3087)1 from 1580 N., 1900 W. All in Sec. 13, T. 47 N., 

 R. 46 W., Michigan. 



Specimen 950S is a bright red jasper, banded wilh very thin seams of brilliantly 

 metallic lustered hematite. Specimen 9509 is a dark brr/^niisli gray cliei't. Specimen 

 9510 is similar to 9508 but is mottled with irregular blotches of red iron oxide. 



The thin section 2983 consists of finely crystalline, mingled with soiiie amor 

 phous silica, in which arc included very numerous minute jia-rticles of liright red 

 hematite, which ar<^ aggregated more fhickly along certain bands. .Many of flie 

 hematite ))articles have rhombic crystal outlines, and apjicar therctiue to have (U'ig- 

 inated from the oxidation of iron carbonate. 



