(iEOLOGIdAL EXrLOKATIONS AND LITERATURE. 43 



the eastward, tUe "white quartz*' and "siliceous dolomitic marlde," are here entirely 

 ab-sent; but tliis fat-t is quite in accord with the rehitions everywlierc t(> be observed 

 between tliesc two widely distiuct rock series. Another fact of iiiiportance is the 

 steady lesseiiiiijj of the disturbing iiitiucnce exerted on the niagiietic needle liy tlie 

 iron belt of the Huronian, as it is followed eastward. In its more western exttinsion 

 the vnriatioiis ol)served on and near this belt are commonly as much as 00° t() ISO"^, 

 the distnrhiiifi' influence exteudiug, moreover, for a Ions distance to the north and 

 south of the line of greatest disturbance. By the time the Potato river is reached 

 the variations never approach 90°, and are to be observed along a very narrow belt 

 only. Still farther east the attraction lessens yet more rapidly, and on the ^Montreal 

 river you have yourself observed that it is essentially lost. This lesseuing in mag- 

 netic attraction does not necessarily indicate a corresponding decrease in the amount 

 of iron present in the rocks of the ii'on belt, but rather that the magnetic oxide is 

 giving way more completely to the nonmagnetic, or sestpiioxidc, which is alwaj'S 

 present, in greater or less (luantity, even where the magnetic attractions are greatest. 

 The outcrops observed bear out this conclusion; for a considerable quantity of \ery 

 highly maiiganiferous red hematite is to be seen at points all along from the passage 

 of Tyler's fork eastward. 



Yet another i)oint of interest brought out by this year's work is the a|)iiarent 

 demonstration of the nonexistence of other magnetic; belts in the indrc nortliern or 

 upper portions of the Ifuronian series. Hematite, or si)ecular ores, may exist hei'e, 

 but the gaps in the series of layers have now been so largelj^ filled up that it appears 

 probable that any discoveries of ore which may l)e made in the future will be on the 

 already known magnetic belt, (Pp. 19-21.) 



Chamberlin (T. C). Annual Report of the Wisconsin State Geologi(!al Sur- 

 vey for the year 1877. Madison, 1878. 



Pages 25 to 28 of this report include a brief account of an examina- 

 tion made l)y Prof T. C. Cliamberlin of that part of the Penokee range 

 which hes between the Potato and Montreal rivers. The following, as to 

 the contact of the basal member of the Iron-bearing series with tlie scliists 

 south of it, is of especial interest: 



At the falls of the Gogogashugun a most interesting section may be made out. 

 The falls themselves are due to the barrier imposed by the siliceous schists that here 

 form the lowest exposed member of the Huronian series. By going back from the 

 falls a short distance, guided by the indications of the loose blocks of rock on the 

 surface, the party were fortunate enough to uncover, at their first attempt, the exact 

 junction between the Laurentian and Huronian series. The Lanrentian member con 

 sists of a peculiar gnei.ssoid rock, altogether like that which occujaes a similar 



