THE MARQUETTE AND MENOMINEE HURONIAN. 393 
of the Marquette and Menominee Huronian are quartzites, magnetitic 
quartzites, rich iron ores, limestones, dolomites, clay-slates, mica-slates 
and greenstones. The greenstones are for the most part diabases with rarer 
gabbro and peridotite. From Wichmann’s microscopic descriptions I judge 
that the same kinds of diabase and gabbro are to be found here as in the 
Animikie Group, though for the most part more altered, i. ¢., the orthoclastic 
and the non-orthoclastic kinds, while the olivinitic kinds are here repre- 
sented by the altered serpentinitic peridotites. 
So far the resemblance to the Penokee and Animikie rocks is striking. 
It is among the remaining less abundant kinds named by Brooks and 
Wichmann, that the seeming lithological differences between the schistose 
systems of these several regions are found. These less abundant kinds 
are: diorite, among the greenstones; syenite; gneiss; granite; sericite-schist; 
jasper-schist and chert-schist; amphibolites, including actinolite-schist, mag- 
netitic actinolite-schist, hornblende-rock and hornblende-schist; augite- 
schist; chlorite-schist; and tale-schist.1 
The diorites of this list I suspect to be mainly uralitic diabases. I 
suspect this on account of the frequency of a uralitic change in the ortho- 
clastic diabases of the Lake Superior region generally; and my suspicion 
is confirmed by the fact that Wichmann finds both augite and uralite as con- 
stituents of his diorites, and speaks distinctly of a gradation between the 
diabase and diorite. Moreover, his descriptions of the diorites make 
them in other points very similar to the uralitic orthoclase-diabases and 
gabbros that I have examined from the Keweenawan and Animikie groups. 
These points are the presence of orthoclase in.greater or less quantity; of 
titanic iron and its gray decomposition-product; of a little quartz, and of 
very abundant apatite. Moreover, the quartz is described by Wichmann as 
occurring in such a way as to “recall the lapis Hebraicus”; a mode of 
occurrence which renders its secondary origin evident,’ and thus seems to 
establish the complete identity of these diorites and my uralitic orthoclase- 
gabbros. 
The syenite‘ mentioned by Brooks and Wichmann as occurring at only 
1Geology of Wisconsin, Vol. II, p. 600. 
2Geology of Wisconsin, Vol. III, p. 627, et seq. 
3Geology of Wisconsin, Vol. III, p. 629, § 91. 
4Geology of Wisconsin, Vol. III, pp. 523, 620. 
