CURRENT PRE-CAMBRIAN LITERATURE 741 
distance upon the Marquette district, the Kona dolomite began to be 
formed, and hence the Mesnard formation is confined to the eastern 
part of the district. The thickness of the Mesnard quartzite is from 
150 to 670 feet. 
The Kona dolomite is largely an altered limestone, but it includes 
interstratified layers of slate, graywacke, and quartzite, with gradation 
phases between these and the pure dolomite. The Kona dolomite, 
like the Mesnard quartzite, is confined to the eastern part of the dis- 
trict. The dolomite varies through a slate into the Mesnard quartzite 
below, and by a lessening of the calcareous constituent gradually 
passes into the Wewe slate above. The thickness is from 425 to 1375 
feel: 
The Wewe slate is chiefly a metamorphosed mudstone, but with 
the slates are conglomerates, quartzites, graywackes, mica-slates, and 
mica-schists. The Wewe slate, like the two previous formations, is 
confined to the eastern part of the district. The formation grades 
into the Kona dolomite below and the Ajibik quartzite above. The 
thickness is from 550 to 1050 feet. 
The Ajibik quartzite, is mainly a metamorphosed sandstone, which 
in different parts of the district, depending upon various conditions, 
has been transformed into quartzite, cherty quartzite, ferruginous 
quartzite, ferruginous cherty quartzite, quartz-rock, and quartzite- 
breccia. The time of the Ajibik quartzite marks a rapid advance to 
the west of the Lower Marquette sea, and therefore the formation 
extends to the western end of the district. In the eastern part of the 
area the Ajibik quartzite grades down into the Wewe slate, but for the 
major part of the district it rests unconformably upon the Basement 
Complex. At many localities contacts and basal conglomerates are 
known. ‘The Ajibik quartzite grades above either into the Siamo slate 
or into the Negaunee iron formation. The thickness is from 700 to 
goo feet. 
The Siamo slate is chiefly an altered mudstone, although locally it 
is a graywacke or quartzite. The larger area of exposure of the forma- 
tion is confined to the eastern part of the district, although a belt of 
the formation runs near the north side of the Marquette series to the 
west end of the district. The Siamo slate grades into the Ajibik 
quartzite below and into the Negaunee iron formation above. The 
thickness is from 600 to 1200 feet. 
The Negaunee iron formation is nonfragmental, heavily ferruginous 
