Lower Marquette Series in Michigan. 



221 



enclosed Archaean areas, hardly leaves room for doubt that 

 they represent the upturned edges of one and the same forma- 

 tion. Furthermore, no other rock is known in the region that 

 is at once so strongly and so uniformly magnetic. The con- 

 clusion therefore is, that the B line like the A represents the 

 lower Marquette actinolite schist. 



It has already been shown that the Michigamme jasper, a 

 magnetic rock, can be traced north from Michigamme Moun- 

 tain, by its magnetic properties, and that when next exposed 

 it has been partly differentiated into a lower quartzite member 

 and an upper member, which alone disturbs the needle, con- 

 taining magnetite and actinolite. Also, that it overlies con- 

 formably an easterly dipping succession, made up below it of 

 nearly 2000 feet of highly altered eruptives and nearly 2000 

 feet of limestone, the whole resting upon Archaean gneisses, 

 to the west. The magnetic line that marks the upper portion 

 of the Michigamme jasper may be called the C line. For 2-J- 

 miles in the northern part of its course the C line runs nearly 

 parallel with, and from \\ to 2 miles west of the B line, where 

 the latter circles round the southwest quarter of its enclosed 

 Archaean oval. This distance of less than two miles, is the 

 interval that now separates the lower Menominee series from 

 the lower Marquette series. A sketch showing the relations 

 in this interesting region is given below. 



The area between the B and C lines is covered and shows no 

 magnetic disturbances. The rock of the C line dips towards 

 the east, that of the B line, in the portion nearest the C line 

 must dip towards the west. They lie then on opposite sides 

 of a trough, and probably are one and the same formation. 



