THE CHERTY LIMESTONE. 129 



R. 5 W., Wisconsin. Farther east we ilo nut meet witli any exposures of the 

 limestone until Sec. 24, T. 44 N., R. 4 W., Wisconsin, southeastward from 

 Bhidder lake, is reached. In tlie interval tlic (inly known rock is a great 

 mass of galjbro. Whether any oi the members of the iron series are 

 here continuous is an open question. The limestone exposure just referred 

 to, which exposure, however, indicates an unusual thickness for the belt, 

 is the only fact we have for the area indicated on the general map as 

 extending through Sees. 23 and 24 of T. 44 N., R. 4 W., Wisconsin, and Sec. 

 19 of T. 44 N., R. 3 W., Wisconsin. So far as exposures go, however, there 

 is nothing to indicate that this area can not l)e continuous with that long one 

 which begins about a mile west of Bad river, in Sec. 15, T. 44 N., R. 

 3 W., Wisconsin. The eastward continuation of the latter area is indicated 

 by several exposures in R. 2 W., and it is possible that there is a connection 

 with the area which is represented as occurring in the vicinity of Tylers 

 fork, in the southerly part of T. 45 N., R. 1 W., Wisconsin. There is, 

 however, -certainly a break in the continuity before the Potato river is 

 reached, for here the Quartz-slate member of the iron-bearing series lies 

 with a marked unconformity directly upon a chloritic schist of the older 

 series. To the east of Potato river only small exposures of the member are 

 met with — one in the middle of T. 45 N., R. 1 E., Wisconsin, and two in T. 

 47 N., R. 46 W., Michigan — until a point some 2 miles east of Sunday lake 

 in Michigan is reached. Through some of this distance the Limestone 

 member nuist certainly be absent, since the exposures of tlie Quartz-slate 

 member and of the lower rocks come into direct contact with one another, 

 as on the West Branch of the Montreal, T. 46 N., R. 2 E., Wisconsin, or so 

 close to one another as to leave no room for the limestone belt. The eastern- 

 most of these limestone areas, that in the eastern part of T. 47 N., R. 45 W., 

 Michigan, and western part of T. 47 N., R. 44 W., Michigan, is one of the 

 most extensive and best exposed in the series. 



Possible former greater continuity. — The occurrence of cherty fragments 

 in the lower portion of the Quartz-slate member of the iron series in places 

 where the limestone with this chert are themselves entirely wanting is 

 strongly suggestive of a former greater continuity for the Limestone member 

 than it now possesses. This occurrence of cherty fragments is frequent 



MON, XIX— 9 



