GENERAl. GKOLOGY OF THE DlStRICT. ' 439 



* 



Quartz-slate is exposeil ; liowevei', tlie cliara'-toristic quartzlte at its upper 

 horizon i.s seen. The iron torniation sliows a praeticalh' continuous expos- 

 ure and at its uppermost horiz(>n is found the peculiar garnetiterous slate, 

 which passes into the yarnetit'erous Ijlack slate at the base of the Up))er 

 slate member just as on the west side of the fault. I'he occurrence of 

 these characteristic layers both north and south of the iron formation — east 

 and west of the supposed fault line — is most fortunate, enabling one 

 to determine the exact limits of that formation and thus to <»ive data 

 for a satisfactory explanation of the distribution. This order is in such per- 

 fect accordance upon both sides of this line that there could be little (hmbt 

 that the belts represented a once continuous set of layers, even if we knew 

 nothing about the series farther to the east and west. But when it is remem- 

 bered that these several belts stretch in the same order for man^' miles in 

 both these directions, this former continuity mav be considered demon- 

 strated. The distribution of exposures at Penokee (lap can then onU be 

 explained as having- been caused by a fault between the two sets of expos- 

 ures, for there is not room between them for accordance to be produced bv 

 a bend of the layers, however sharp. Tlie space l)et\veen the (juartz-slates 

 on the west side of the fault and the upper part of the iron formation on 

 the east side is not one-half the thickne.ss of the latter, vet between these 

 two the whole of it must pass if there is not here a fault. The Quartz-.slate 

 on the west is seen to be farther lutrtli than the iiorthermnost exjjosure of 

 the magnetite schists, toward which it strikes, whereas it ought to be con- 

 tinuous with the belt of the sam(^ kind on the east siile of the line marked 

 "supposed line of fault." 'ilie amount of disconlanee is even more strik- 

 ingly shown by the positions of the exposures of the iron formation. It may 

 be that a part of the discordance can l)e accounted for l)v a sudden l)owing 

 of the layers, although the strike of the rock gives little in<lication that this 

 is the case. If the entire dislocation is taken to be due to a fault, the throw 

 must have been at least 900 feet if at i-iylit any-les to the direction of the 

 strike of the rocks; and if it is diagonal, as is probablv the case, must have 

 been more than this. 'That this fault extends south (jf tlie southernmost 

 exposure of the Penokee series and north of the expo.sures of the basement 

 layer of the black slate is plain, l>ut the layers of the upper slate are so 



