524 TUE MARQUETTE lEON-BEAEING DISTRICT. 



Complex and tlie Marquette .series. They are in the main uonfoliated, 

 even where the rocks into which they are iuti-usive are well-characterized 

 schists. For these reasons they are separated from the older greenstones, 

 and because they are very similar to the basic rocks of the Keweenawan 

 series on Keweenaw Point they are thought to be the equivalents of some 

 of the Keweenawan eruptives. 



These greenstones comprise oli-sdne-diabases and quartz-diabases, por- 

 phyrites, and basalts. Of these the porphyrites are most like the older 

 greenstones, from which they are distinguished by clear-cut and well- 

 preserved porphyritic structure. The basalts are like modern basalts, except 

 that their groundmass is always much altered. The olivine-diabases are 

 typical rocks of this class. The quartz-diabases are peculiar in that they 

 contain a little olivine and sometimes a large quantity of quartz, which 

 occurs in micropegmatitic iutergrowths with plagioclase. 



None of the larger masses of the greenstones of the older or the 

 younger kinds are in the form of great interbedded sheets, as has been 

 stated to be the case by the earlier geologists. The sheets that do occur 

 are thin, and, so far as known, they are not continuous for long distances, 

 nor do they appear to occupy any distinct and definite horizons in the 

 bedded series outside of the Clarksburg formation. 



