eckel.] MICHIGAN. 201 
Analysis of the ash. 
Silica. (Si0 2 ) - 70.54 
Alumina (A1 2 3 ) 15.33 
Ferric oxide (Fe 2 3 ) 5. 31 
Calcium (CaO j 2. 38 
Magnesium (MgO) 78 
Alkalies, etc., by difference 5. 56 
Total 100. 00 
As remarked by Ries, the ratio' of silica to alumina in this analysis is unusually 
high, but so far as can be judged this material is worth careful investigation on the 
part of cement makers. 
The Antrim shales are exposed on the shore of Thunder Bay, and also at several 
localities in Charlevoix County, where they are associated with marl deposits. The 
availability of these shales in manufacturing Portland cement and the utilization of 
the organic matter they contain as a by-product seems to be a possibility worthy of 
consideration. 
SAGINAW FORMATION. 
The shales of the coal-bearing rocks which underlie an extensive area in the central 
portion of the southern peninsula, and are well developed in the productive coal 
field of the Saginaw Valley, although frequently containing sand, have in some 
instances approximately the physical and chemical composition desired in cement 
making. The fact that these shales are frequently removed in the process of coal 
mining and that facilities for transportation are available claim for them careful 
attention as a source of material for use in manufacturing Portland cement. 
As stated by Ries, a three types of shale in the Saginaw formation may be recog- 
nized, between which there are intermediate gradations. These are — 
First. A light-gray, sandy, shaly clay, often quite hard, called "fire clay," and 
not infrequently containing fossil plants. Shale of this character is present beneath 
a coal seam at the mines of the Standard Mining Company, near Saginaw, and has 
the following composition: 
Analysis of shale from Saginaw. 
[Analyst, H. Ries.] 
Silica ( Si0 2 ) 55. 30 
Alumina ( A1 2 3 ) 14. 20 
[Ferric oxide (Fe 2 3 ) 3. 62 
Calcium carbonate (CaC0 3 )| 30 
^Magnesium carbonate (MgC0 3 ) 2. 61 
Alkalies (K 2 0, Na 2 G) 2. 15 
Water and organic matter 21. 82 
Total 100. 00 
Fluxes 8. 68 
This shale is evidently too low in alumina and iron in proportion to the silica 
(present to be used to advantage in the manufacture of Portland cement as now 
'practiced. 
l! Second. A black, fine-grained, brittle shale, with dull luster, sometimes termed 
"cannel coal." It contains much bituminous matter and would not serve well for 
the manufacture of clay products (Ries). 
aGeol. Survey Michigan, vol. 8, pt. 1, 1900, pp. 25-38. 
