4 THE MARQUETTE lEOX-BEAKING DISTRICT. 



in passing from the sides of the trough toward the center newer rock appear 

 rather than older ones, so that in the center of the synclinoriuni the 

 youngest rocks are found. It is as if the composed fan folds of the Alps 

 were sagged downward, so that the structure as a whole is a synclinoriuni 

 rather than an anticlinoriuni. The structure thus differs from the composed 

 fan structure of the Alps and from the inverted intermout trough of 

 Lapworth, and may be called an abnormal synclinorium^ (fig. 1). This 

 structure prevails in the central part of the area from Islipeming and 

 Negaunee westward to Clarksburg, but it does not extend to Lake Su^jerior 

 on the east nor to Lake Michigamme on the west. 



Fin. 1. — Generalized c 



i-section of Marquette aynel 



, showing tlio Afarquetto type of fold. 



"While the more conspicuous folds have in general an east-west direction, 

 the rocks have also been under strong east-^vest compression, as a conse- 

 quence of AvhicU the folds are buckled so that they often show a steep pitch. 

 In places the north-south folds become more prominent than the east-west 

 folds, and control the prevalent strikes and dips. In aii intermediate area 

 the two series of folds are about equally important, thus producing most 

 irregular strikes and dips. These north-south folds are of two orders: the 

 first of great magnitude, but small dip; the second, superimposed on the 

 first, of less length of wave, but with steeper dip. 



'Principles of Nortli American pre-Cambrian geology, by C. K. Van Hise: Sixteenth Ann. Kept. 

 U. S. Geol. Survey, Part I, 1896, pp. 612, 616-620. 



