OF SOME HURONIAN CLAY-SLATES. 
157 
Huronian Systm. 
T. B. Brooxs*. 
I. ) 
II. 
LT: 
IV. 
Beds of siliceous ferrugi- 
nous schists, alternating 
with chloritie schists and 
diorite. 
) 
V. Quartzite, sometimes con- 
taining marble and beds 
ofargilliteand novaculite. 
VI. 
VIII. | Siliceousferruginousschists. 
X. 
VII. 
IX. | Dioritic rocks. 
xy 
XIII. Specular and magnetic ore 
associated with mixed ore 
and magnesian schist. 
XIV. Quartzite often conglome- 
ratic. 
XV. Clay-slate or argillite. 
XVI. Uncertain: it contains some- 
times some soft hematite. 
XVII. Anthophyllitic schist con- 
taining iron and man- 
ganese. 
XVIII. Doubtful. 
XIX. Mica - schist, containing 
staurolite,  andalusite, 
and garnets. 
“XX. Granitef. 
I. 
II. 
Ii. 
VI. 
VII. 
XII. 
Herm. Crepnert. 
Quartzite and chlorite \ 
Schiistssipsemecuse. canes 
Diorites alternating 
with siliceous, fer- 
ruginous, and man- 
ganous schists and feet. 
quartzite ........ see | 2500-3500 
Taleose and chloritic 
schists and magnetic 
ivon-Ore ............... 
Siliceous ferruginous 
schists and specular 
ore with beds of ser- 
POSIT Gondnooodooodcs 
Crystalline | 
limestone, 
contain- 
ing beds of clay-slate | 5 
ral chlorite schists ; r 2900-3000 
many layers of 
quartzite 
Siliceous ferruginous 
schists 
600-1000 
Cesc er te se neces 
Chlorite schists with 
beds of ferruginous 
schists 
1200 
eee cee ceraesoe 
8500 
beds of quartzite . 
Chlorite schists with } 
beds of diorite.. 
Talcose schists nein: 
ing dolomitic lime- 
stone, quartz-schists, 
and beds of diorite. 
(Dioritie near e cece 
1300 
Clay-slate containing a 
a 
oe 
T. B. Brooks, in his classification, refers solely to the conditions of 
the Marquette region, because the concordance with the Menominee 
region is not yet ascertained. 
A. Clay-slate §. 
Hardly any difference can be perceived between the external ap- 
pearance of these rocks and those of later periods. 
* Michigan Geolog. Survey, vol. i. p. 83. 
+ Amer. Journ. of Science and Arts, vol. xi. March 1875, 
§ Mich. Geol. Survey, vol. i. p. 111. 
Although their 
t+ Loe. cit. 
