90 THE MAKQUETTE IKON-BEAIJING DISTRICT. 



directly, but very often iueoiifi)rmably, on cUlorito-bydro-micaceous scbists, or on 

 crystalHue dioritic masses wbicb are constant associates of these chloritic scbists, or 

 sometimes dioritic scliists, as bornblende and cldorite substitute eacb other, or are 

 both components of them. 



Overlooking the extremely plicated and corruyated condition of the strata, 

 they form, considered in their totality, a synclinal basin hemmed in between dioritic 

 ridges. (Pp. 72-73.) 



After (k'scrihini;- the general structural t'eatitres of the <»re t'orniatiou 

 Rouiiug'er jjroceeds to de.scribe the ditfereut mmes, givmg details too 

 uumerotts to mention in this review. He heg'in.s with the Jackson mine, 

 which he saA-s is in the upper jiart of the formation whose lower portion 

 is fou.nd on the diorite hills south of Negaiuiee. The ores are in a banded 

 jasper rock, and are usually associated with "belts of argillitic schists called 

 soapstone by the miners." The ore bodies are irregularly distribtited 

 through the jasper-hematite-schists, except that — 



a very rich seam of ore is almost invariably found on top of this jasper-banded rock- 

 serie.s. immediately beneath the quartzites which form the terminal strata iu all these 

 exposures. This upper ore belt is almost regularly brecciated iu its upper part, and 

 the same is true of the lower (juartzite beds, which often are a mixture of ore frag- 

 ments with quartzite pieces held together by an arenaceous cement. As this is the 

 case iu nearly alf the mines of the district, we nuist suggest that great disturbances, 

 of not only a local extent, must have occurred at the end of this era of irou sedi- 

 ments. (P. 74.) 



In another part of the series, it is declared, there is a great thickness 

 of argillitic rocks, all impregnated with red oxide of iron, and in these are 

 intercalated ore seams in such quantity as to make this one of the most 

 productive fields for the miner. 



These ore deposits are not regular sedimentary layers, originally formed of iron 

 oxide in this state of purity, but are evidently the product of decomposition of the 

 impurer mixed ferruginous ledges by percolating water, leaching out the siliceous 

 matter and replacing it by deposition of oxide of iron held in solution. (P. 75.) 



The ores are dark or yellow soft ores, composed parth' of hydrated 

 and partly of noidiydrated oxide, and containing often globular and con- 

 cretionary masses with a radiating or fibrous structure or "with the granular 

 crystalline form of goethite." Pj-rolusite and other manganese compounds, 



