746 C. KE SERIGEE, 
particularly occurs in the west and southwest parts of the district, west 
of Champion and along the Republic Trough, where but few mem- 
bers of the Lower Marquette series were deposited. Even within a 
short distance the differential erosion was considerable. For instance, 
at the south end of the Republic Trough the variation was more than 
1500 feet. 
The Marquette district has been folded in acomplex manner. ‘The 
largest but least conspicuous fold of the district is an anticline having 
a north-south axis, running through the city of Marquette. This great 
fold has, especially near its crown —that is, for the eastern six or eight 
miles of the district—folds of the second order superimposed upon it, 
making this part of the fold an anticlinorium. The other major anti- 
cline belonging to this system of folds is one running north and south 
through the east end of Michigamme Lake. The major part of the 
district has been affected, however, by much more effective pressure 
in a north-south direction, so that the folds in an east-west direction 
are much more conspicuous than the north-south folds of greater wave- 
length and greater amplitude. As a result of the north-south pressure, 
the Upper and Lower Marquette series together have been bent into a 
great abnormal synclinorium. ‘This synclinorium is of a peculiar and 
complicated character. ‘he Algonkian rocks on either side of the 
trough have moved over the more rigid Archean granite, and, as a 
consequence, on each side of the Algonkian trough a series of over- 
folds plunge steeply toward its center, producing a structure resem- 
bling in this respect the composed fan structure of the Alps. ‘There is, 
however, this great difference between the Marquette structure and that 
of the Alps, that in passing froin the sides of, the trough toward the 
center, newer rocks appear rather than older ones, so that in the center 
of the synclinorium the youngest rocks are found. It is as if the com- 
posed fan folds of the Alps were sagged downward, so that the struc- 
ture as a whole is a synclinorium rather than an anticlinorium. This 
form of folding has been elsewhere defined by Van Hise’ as an abnor- 
mal synclinorium. The folding is closer in the western part of the 
district than to the east. The strikes of most of the exposures of the 
district are mainly controlled by the east-west folds, but, at the east 
and west ends of the areas of the formations, the larger north-south 
folds already described control. 
*Principles of North American Pre-Cambrian geology, by C. R. VAN HISsE, 
16th Annual Report U.S. Geol Surv., Part I, 1896, p. 612. 
