THE IKON-BEARING MEMP.ER. 191 



the appearance of liaviiio; been ln-okeii apart and receineiited, in which case 

 there is. usually a considerable ([uantity ol' the chertv silica ])rescut. The 

 observations thus far made have ap])lied particularh' to fresh surfaces. On 

 e.xposed surfaces there is very ai)t to be a prevalent brownish or re(Mish iron 

 stain from peroxidation of tlic iron of the carbonaic. In spccilic <j;'ravitv 

 these rocks range generally l)etween the two precedinj^' t\pcs. 'i'lic specitic 

 gravity of pure iron cafl)onate is given in the mineralogies as Itetween 3"7 

 and .'V!). The rocks now considered iall l)elo\v this figure because of the 

 presence of other ligliter substances, particularly the calcareous, siliceous 

 and clayey ingredients. The following figures are the i-esnlts f>f specitic 

 gravity determinations: 2-97, 3()4, 320, .3-22, 324, 329, 3-40, and 350. 



Of the following analyses the tirst five icpresenf the comjjosition of 

 iron carbonates from the Penokee-Gogebic district. The remainder are of 

 similai- carbonates from other districts about lake Superior, ami ai'e inserted 

 here tor the sake of comparison. No. 1 (specimen 111 Itl), anal\/,e(| l)y Mr 

 K. B. Kiggs, of the U. S. Geological Snrve\-, is of a rock exposed in a 

 test-i)it in the NE. \ of the NK. ', of Sec. (I, T. 4') N., \i. 2 iv, Wisconsin. 

 No. 11 (specimen !)472), made by Mr. W F. llillel)rand, of the U. S. Geo- 

 logical Survey, is of a s|)ecimen from the large ])r('ci])itous exposure on 

 the south side of the outlet of Sunday lake, XK. ] of Sec. 13, T. 47 N., K. 

 4n W., Michigan. No. Ill (specimen 12S,s:)), nuide by 3Ir. Thomas M. 

 ("hatanl, of the IL S. Geoktgical Siu-vev, is n\' a cai'iionate occurring near 

 the i)ase of the Inm-bearing meml)er on the .Miner iSc Wells npti.m. Sec. 13, 

 T. 47 N., R. 4fi W., Michigan. Xo. I\' (specimen i2S,S7), made by .Mr, llil- 

 lebrand, is of a specimen representing- a large natmal exposure on tlie 

 I'alms property, »Sec. 14, T. 47 N., R. 4(1 W., .Michigan. Xo, \' (speci- 

 . men 12543), made by Mr. Chatard, represents a carbonate occnning at a 

 low horizon in the meml)er, in the XW. ', nf Sec. IS, 'I\ 47 N., K', lo W., 

 Michigan. Of the remaining analyses, Xo. \'l (specimen Il2(j4), b\ Mr. llil- 

 lebrand, represents a ))eculiar carbonate occin-ring in the SE. 4 of Sec. 20, 

 T. .47 N., R. 43 W., Michigan, in that confused area to the east of the Presque 

 Isle river, which is considered in the present \(ilume separateh- from the 

 regular I'enokee succession. No. VH (specimen 1007.')), b^■ .Mr ('liatard, 

 is an iron carbonate from the so-called g-mifiint lieds exposed on tlu eastern 



