214 THE PENOKEE IRON BEARING SERIES. 



quite pleutit'ull}- as an alteration product of" the rtctiut)lite. In some 

 cases brown iron oxide stains tlie actintdite blades. A separation of 

 the garliet (specimen 9553) by W. 8. Bayley having been made, the 

 following- analysis' of the separated material was made by Dr. Gliomas 

 M. Chatard, of the laboratory of the U. 8. Geological Survey: Silica, 

 39-31; alumina., 12'S<); iron .?esquioxide, 1021; iron protoxide, 32S1; 

 nianganous oxide, 1'03 ; calcium oxide, 1'88 ; magnesium oxide, 

 1-90 = 100-00. Dr. Chatard observes that this analysis is close to that 

 of an averao'e almandite. At one time in our stud\' of this rock 

 it was supposed that the actinolitie ingredient might he the result of a 

 secondary alteration of the garnet, l)ut the abundance of the same actino- 

 lite in the underlying magnetitic and actinolitie schists with which this 

 rock is so intimately associated, and in Avhich the actinolite is surel\- not an 

 alteration product of garnet, seemed to render such an origin improbable. 

 A further study of the sections appears to show that the actinolite, even in 

 the garnetiferous rock itself, is independent of the garnet, lia\ing l)een in 

 part a simultaneous crystallization and in part an earlier crystalliza- 

 tion. This conclusion is borne out by the analysis above quoted, from 

 which it appears that the composition of this garnet is such that the actino- 

 lite could not readily have been derived from it. Immediately over- 

 lying this garnetiferous rock is found a black fragmental slate." At the 

 junction between the two the garnets are found to occur within the frag- 

 mental material, an occurrence which suggests the possibilitv that tliis frag- 

 mental material turnished some f)f the ingredients Avhich subsequent!}' 

 made up the garnet. 



'With reg.aril to thiH iiuiilvsis Dr. Chatard .says that the amount of material fuiuishcul was 

 only 1.2 gram.s, and tliat owing to the loss of a portion there remained hut 0.54 gram lor the 

 determiuatiou of the ab.S(dnt(' amount of inm protoxide. This remnant heiug too small f<n' the deter- 

 mination, the iron protoxide was calrnlated from the excess over 100 in the snnimatiou of the entire 

 analysis after estinuiting all the iron as the sesqnioxide. Dr. Chatard also says that this methi>d of 

 rahulation -'gives a result <dose to the average analysis of aliuanilite garnet, which the mineral 

 .mdonlitedly is." 



■ For an early descriplion of this garnetiferous slate, whieh, thou'ili not fn'(|nently met with in 

 the Penokee region, is closely iilli(Ml to certain garnetiferous ;ietiuolitie schists oi'enrring nu)re 

 wiilely in the Maninette n^giou of Michigan, see Geol. of Wis., vol. ill, pp. 128, 124; see also for 

 rude colored drawings of the thin sections of the same rocks, Figs. 1 and 2 of PI. xva of the same 

 volume. 



