THE IRON-BEARING MEMBER. 199 



statement that the transitidu between the cherty phases and the car- 

 b(«iates is a regular or sharp one, as the carbonates sink to hiwer 

 horizons in some phices, while the chei'ts rise to higher in others 

 but merely that exposures and the numerous test pit explorations show 

 that there is this general arrangement. It is thought that this arrange- 

 ment has a connection with the origin of the ore bodies, for which an expla- 

 nation is attempted on a subsequent page. It should be said that this 

 arrangement is much more definitely made out through T. 47 N., R. 46 and 

 R. 47 W., Michigan, than it is farther to the west in Wisconsin, where the 

 explorations have been fewer. So far as exposui-es have been found west of 

 the state line, they indicate the contiiuiit}' of this succession westward to 

 beyond the Potato river ci-ossing. The succession as seen in T. 47 N., 

 R. 46 W., Michigan, may ])e described more fully as follows: Beginning 

 with the uppermost portion of the belt, we find the finely laminated, little 

 altered siderite rocks to prevail. As these are crossed to the south, more 

 and more red hematite rei)laces the iron carljonate, until finally little or no 

 unoxidized carbonate remains. Here the rock is a reddish slaty one, often 

 preserving quite perfectly the original regular lamination, but the only con- 

 stituents are more or less hydrated hematite and silica. Still farther south- 

 ward the lamination becomes less and less distinct and regular; the amount 

 of silica rapidly increases, and the rock passes into the ferruginous chert 

 of the second type in which the iron oxide is contained in irregular blotches 

 and noncontinuous bands. Finally, at the base of the formation the iron 

 oxide is collected often into large bodies, which generally lie directly against 

 the quartzite, the uppermost horizon of the Quartz-slate member. 



Following the iron belt now farther east\vard into T. 47 N., R. 45 W., 

 Michigan, another change is met with — the actinolitic and magnetitic rocks 

 of the third type coming in plentifully. At first these occur along with 

 both the ferruginous cherts and carbonates, but as one passes farther 

 eastward no more carbonates are met with, the actinolitic schists and ferru- 

 ginous cherts only beiny found. The latter in turn lessen in amount, the 

 actinolitic schists being more and more plentiful until in the exposures 

 near the Little Presque Isle river, in T. 47 N., R. 44 AV., Michigan, they are 

 the only kinds met witli. This transition from the predominance of the 



